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Korean Society of Life Science (한국생명과학회)
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Regulation of Cinnamyl Alcohol Dehydrogenase (CAD) Gene Family in Lignin Biosynthesis

리그닌 생합성에서 cinnamyl alcohol dehydrogenase (CAD) 유전자 family의 조절

  • Kim, Young-Hwa (Ubiquitous Healthcare Research Center, Inje University) ;
  • Huh, Gyung-Hye (Ubiquitous Healthcare Research Center, Inje University)
  • 김영화 (인제대학교 U-항노화헬스케어연구소) ;
  • 허경혜 (인제대학교 U-항노화헬스케어연구소)
  • Received : 2021.09.07
  • Accepted : 2021.09.30
  • Published : 2021.10.30
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Abstract

Lignin is a complex phenylpropanoid polymer abundant in the cell walls of vascular plants. It is mainly presented in conducting and supporting tissues, assisting in water transport and mechanical strength. Lignification is also utilized as a defense mechanism against pathogen infection or wounding to protect plant tissues. The monolignol precursors of lignin are synthesized by cinnamyl alcohol dehydrogenase (CAD). CAD catalyzes cinnamaldehydes to cinnamyl alcohols, such as p-coumaryl, coniferyl, and sinapyl alcohols. CAD exists as a multigenic family in angiosperms, and CAD isoforms with different functions have been identified in different plant species. Multiple isoforms of CAD genes are differentially expressed during development and upon environmental cues. CAD enzymes having different functions have been found so far, showing that one of its isoforms may be involved in developmental lignification, whereas others may affect the composition of defensive lignins and other wall-bound phenolics. Substrate specificity appears differently depending on the CAD isoform, which contributes to revealing the biochemical properties of CAD proteins that regulate lignin synthesis. In this review, details regarding the expression and regulation of the CAD family in lignin biosynthesis are discussed. The isoforms of the CAD multigenic family have complex genetic regulation, and the signaling pathway and stress responses of plant development are closely linked. The synthesis of monolignol by CAD genes is likely to be regulated by development and environmental cues as well.

리그닌은 식물의 세포벽에 풍부하게 존재하는 복잡한 phenylpropanoid 중합체이다. 주로 물 수송과 기계적 강도를 유지하는 조직에 존재하며 수분을 운반하거나, 기계적인 지지를 담당한다. 또한, 리그닌은 병원균의 감염이나 상처에 대한 물리적인 장벽으로 작용함으로써 방어 기작에 관여한다. 리그닌을 생성하는 모노리그놀 전구체는 cinnamyl alcohol dehydrogenase (CAD) 유전자에 의해 합성된다. CAD는 cinnamaldehyde를 cinnamyl alcohol(p-coumaryl, coniferyl, sinapyl alcohol)로 전환하는 효소이다. CAD는 속씨식물에서 multigenic family로 존재하며 여러 식물 종에서 다른 기능을 가진 CAD isoform이 밝혀졌다. CAD 유전자의 여러 isoform은 식물의 발달 및 환경 신호에 따라 다르게 발현되었다. 하나의 isoform이 발달 리그닌화에 관여하는 반면, 다른 isoform은 방어 리그닌 및 기타 세포벽에 결합된 페놀의 구성에 영향을 미칠 수 있음을 보여주었다. CAD isoform에 따라 기질 특이성이 다르게 나타나고, 이는 리그닌 합성을 조절하는 CAD 단백질의 생화학적 특성을 나타내는데 기여한다. 본 논문에서는 리그닌 생합성에서 CAD multigenic family 유전자의 발현과 조절에 대하여 설명하였다. CAD multigenic family의 isoform들은 유전적 조절이 복잡하고, 식물 발달 과정의 신호 경로와 스트레스 반응이 밀접하게 연동되어 있다. CAD 유전자에 의한 모노리그놀 합성은 발달 및 환경 신호에 의해 조절될 가능성이 높다.

Keywords

Lignin biosynthetic pathway

Lignin is the most abundant organic polymer found in nature after cellulose. It is a complex biopolymer deposited in the cell walls for water transport and mechanical strength. The phenylpropanoids, hydroxycinnamyl alcohol and monolignols (ρ-coumaryl, coniferyl, and sinapyl alcohol) account for most of the lignin network [3].

Lignin biosynthesis comprises a highly coordinated and regulated metabolic activity, and many enzymes are involved in this pathway. Phenylalanine ammonia-lyase (PAL) produce cinnamic acid, which acts as a substrate for cinna-mate-4-hydroxylase (C4H). C4H produces p-coumaric acid and successively caffeic acid by p-coumarate-3-hydroxylase (C3H). The caffeic acid is methylated to produce ferulic acid by caffeic acid O-methyltransferase (COMT). The CoA esters of p-coumaric acid, caffeic acid, ferulic acid, 5-hydroxyferulic acid and sinapic acid are produced by 4-coumarate-CoA ligase (4CL). The p-coumaryl CoA, feruloyl CoA, and sinapoyl CoA are considered as substrates for cinnamyl-CoA reductase (CCR), which can produce the corresponding aldehyde. These aldehydes are substrates for cinnamyl alcohol dehydrogenase (CAD) producing the three monolignols (Fig. 1A). The three monolignol precursors are different in their degree of methoxylation, that is, p-coumaryl (non-methoxy-lated), coniferyl (monomethoxylated), and sinapyl (dimoth- oxylated) alcohols (Fig. 1B). This diversity of subunit substitution indicates that a variety of intermolecular linkages can be made during polymerization [3]. Then, they are oxidized by peroxidase or laccase to form the lignin polymer. The common phenylpropanoid pathway provides the hy- droxycinnamoyl-CoAs, which are converted into the monolignols through the lignin specific pathway [44]. Lignin specific pathway involves two enzymes, CCR and CAD, which convert the hydroxycinnamoyl-CoA esters into monolignols [45].

SMGHBM_2021_v31n10_944_f0001.png 이미지

Fig. 1. A. The lignin biosynthetic pathway. B. Structure of most common lignin monomers. PAL, phenylalanine ammonialyase; C4H, cinnamate-4-hydroxylase; C3H, p-coumarate-3-hydroxylase; COMT, caffeic acid 3-O-methyltransferase; CCoAOMT, caf- feoyl-CoA 3-O-methyltransferase; F5H, ferulate-5-hydroxylase; 4CL, 4-coumarate CoA-ligase; CCR, cinnamoyl-CoA reductase; CAD, cinnamyl alcohol dehydrogenase.

Lignin biosynthetic CCR gene

The CCR is the first step in the monolignol specific path- way, by converting hydroxycinnamoyl-CoA esters to their corresponding aldehydes. CCR is encoded by a single gene in Eucalyptus gunnii (EgCCR) and perennial ryegrass Lolium perenne (LpCCR). EgCCR mRNA was expressed in xylem, supporting the role of the enzyme in lignification. EgCCR was also strongly expressed in less lignified leaves [23]. LpCCR mRNA was expressed in all organs, but was most abundant in lignified organs. LpCCR was stimulated by mechanical wounding [35]. Two CCR isoforms have been characterized in Zea mays [36] and Arabidopsis thaliana [25]. In different tissues of maize, ZmCCR1 was involved in developmental lignification, while the ZmCCR2 was expressed only in roots and involved in stress responses. Arabidopsis AtCCR1 was mostly expressed in tissues undergoing lignification, which was involved in constitutive lignification. But, AtCCR2 was nearly expressed during development, but strongly induced by pathogen treatment. It contributed to biotic stress resistance by producing phenolics. There are differences in function between members of CCR gene in angiosperm species.

Lignin biosynthetic CAD gene

At the end of the monolignol biosynthetic pathway, CAD catalyzed the reduction of hydroxycinnamyl aldehydes (p-coumaraldehyde, coniferaldehyde, and sinapaldehyde). It was an important enzyme in lignin biosynthesis and has been studied in many plant species. CAD gene was abundantly expressed in developing xylem. It can be explained that secondary walls of xylem cell are the important site of lignin synthesis during plant development. On the other hand, CAD genes are involved in defense response or metabolic processes not related to the developmental lignification of the vascular tissue. CAD is responded to stress by hardening the cell wall. When wheat leaves were treated with fungi elicitor, CAD activity was highly increased and sinapyl alcohol was oxidized, specifically. It was enriched in syringyl (S) units in response to pathogens, and CAD could play a role in the control of defense lignin synthesis [34]. In pine (Pinus banksiana) cell culture, fungi elicitor was induced lignification. Following elicitation, it accumulated guaiacyl (G) lignin with change in monolignol biosynthetic enzyme activity [6]. Therefore, CAD is an important indicator for lignification during development and plant stress responses [24].

Knockout and overexpression of CAD gene

Transgenic plants and natural mutants of lignin biosynthetic genes can provide a good source to understand the lignification process. The role of CAD in lignin biosynthesis has been addressed by studies of natural mutants and genetically engineered antisense CAD mutants in various plants [2, 7, 12]. In case of down-regulating CAD activity, transgenic tobacco plants were strongly decreased in CAD activity and insignificant change of lignin content [12]. The composition of lignin subunit was specifically altered, and the proportion of cinnamaldehyde was significantly increased. In pine (Pinus taeda L.) CAD mutant (cad-n1), CAD activity was severely reduced and decreased lignin content [33]. Double mutants of developmental CADs (AtCAD4 and AtCAD5) were characterized in Arabidopsis. CAD activities were greatly reduced and lignin composition was also modified [42]. Natural CAD-deficient mutant bm1 of maize showed a lower lignin content than normal genotype and better digestibility [13]. gold hull and internode2 (gh2) mutant is a brown midrib1 (bm1) orthologue in rice and identified to a lignin-deficient mutant. It exhibits a reddish-brown pigmentation in the hull and internode, instead of the midrib. flexible culm1 (fc1) mutant in rice has deficiency of the OsCAD7 and caused a reduction in cell wall thickness and lignin content. CAD enzyme activity was also reduced [28].

There have been a few reports on overexpression of the CAD gene in transgenic plants. In the case of CAD associated with developmental lignification, rice FC1 gene and sweet wormwood (Artemisia annua) AaCAD gene have been over expressed in planta [28,31]. Overexpression of FC1 did not affect the lignin content of cell walls, while AaCAD showed remarkably higher lignin content in transgenic plants. Mean- while, in case of stress-related CAD, overexpressing wheat TaCAD12 related to a defense lignin was contributed to host resistance against fungi [38]. Overexpression of IbCAD1 from sweetpotato in Arabidopsis plants, which is responded in environmental stresses and involved in developmental lignification, clearly affected lignin content and composition by controlling lignin biosynthesis. The IbCAD1 activity was increased in transgenic plants. It was shown that enhanced tolerance to ROS stresses [22].

Analysis of expression pattern for CAD gene family

CAD gene family has been isolated from various higher plants. The expression of CAD family is diverse with tissue types and developmental stages of the plant. CAD genes showed high sequence homology (~70%) between gymnosperm and angiosperm, suggesting that those are very well conserved during evolution [4]. In gymnosperm, CAD is a single gene and coniferaldehyde-specific [32]. In contrast, multiple CAD isoforms have been isolated from many angio- sperms, and catalyze the reduction of both coniferaldehyde and sinapaldehyde. The expression of CAD family genes varied according to tissue types and developmental stages of the plant. The expression characteristics of the CAD genes are summarized in Table 1.

Table 1. Characterization of CAD family in several plant species

SMGHBM_2021_v31n10_944_t0001.png 이미지

-/+, very weak; +, weak; ++, medium; +++, strong; ++++, very strong; N/D, not detected.

*, not determined.

Kim et al. [18] classified the Arabidopsis CAD multigene family (AtCAD1-AtCAD9) through the kinetic properties and substrate specificities to establish physiological functions. AtCAD4 and AtCAD5 are involved in developmental lignifi- cation. AtCAD7 and AtCAD8 are induced in response to pathogen infection. Detectable CAD catalytic activities of AtCAD1, AtCAD6, and AtCAD9 are not presented [17].

There are 12 OsCADs genes in rice (Oryza sativa) genome, of which OsCAD2 is similar to CAD gene present at the bm1 locus of maize. CAD-deficient mutant bm1 was associated with developmental lignification showing lower lignin content [43]. gh2 mutant was also identified as lignin-deficient in rice [46]. GH2 gene, which encodes a CAD, was defined as OsCAD2. OsCAD2 is constitutively expressed throughout all developmental stages, being most highly expressed in actively lignifying tissues. The expression of OsCAD2 was also induced by biotic and abiotic stresses, suggesting that it plays a role in the defense response [36]. fc1 mutant caused by T-DNA insertion into OsCAD7 gene decreased secondary cell wall thickness and mechanical strength. FC1 showed strong CAD activity that affects the mechanical strength of rice culms [28]. The expression of OsCAD6 was stimulated by pathogen infection and UV-irradiation, which was involved in the defense response of rice against biotic and abiotic stresses [36].

Fourteen SbCAD genes were characterized from the analysis of sorghum (Sorghum bicolor) genome. Based on the phylogenetic relationship with other species CADs, SbCAD2 was involved in lignification, such as developmental CADs including AtCAD4, AtCAD5, and OsCAD2 [39]. In perennial grass (Lolium perenne), three CAD genes (LpCAD1, LpCAD2, and LpCAD3) were identified. LpCAD3 was involved in developmental lignin biosynthesis, but LpCAD1 and LpCAD2 were more closely to other CADs related defense lignification or other functions [29]. Two enzymes, EgCAD1 and EgCAD2, were identified in Eucalyptus gunnii [9]. EgCAD1 has substrate specificity with coniferaldehyde and involved in G lignin synthesis. On the other hand, EgCAD2 can synthesize all three monolignols. MsaCAD1 and Msa CAD2 were isolated from alfafa (Medicago sativa). MsaCAD1 encoded a benzaldehyde dehydrogenase, which was associated with defense response to pathogen. MsaCAD2 catalyzed the reduction of coniferaldehyde and sinapaldehyde [5]. PtSAD is a gene encoding sinapyl alcohol dehydrogenase from poplar (Populus tremuloides). It was phylogenetically distinct from PtCAD. Two genes were synthesized the S and G lignin differently. Specifically, PtSAD was required for the biosynthesis of S lignin in plants [27].

Five CAD genes, CmCAD1 to CmCAD5, were identified in the genome of melons (Cucumis melo L.). CmCAD1 and CmCAD2 belonged to the bona fide CAD group, involved in developmental lignin synthesis. Except CmCAD4, the other CmCADs were highly expressed in young tissues. CmCAD4 was not expressed or expressed at very low levels in these tissues [16]. The PoptrCADs gene family in poplar (Poplus trichocarpa) were sorted into four groups by expression pattern. PoptrCAD4 and PoptrCAD10 in Group I were strongly expressed in xylem and significantly different from the other three groups. PoptrCAD7, PoptrCAD12 and PoptrCAD13 in Group II were expressed in all tissues, particularly high in leaves. PoptrCAD9 in Group III was preferentially expressed in leaves and xylem. PoptrCAD2, PoptrCAD3, PoptrCAD5, PoptrCAD6, PoptrCAD11, PoptrCAD14, and PoptrCAD15 in Group IV showed a similar expression pattern in all tissues [1].

The expression of ZmCAD2 in maize (Zea mays) was shown to be excessively affected in the bm1 mutant, resulting in modified lignin content and structure [13]. Six other CAD family genes were identified according to maize cell wall database [11]. Eleven wheat (Triticum aestivum) CAD isoforms were obtained from wheat EST database. TaCAD1 belonged to the developmental CAD group involved in lignin synthesis. It was highly expressed in stem, with quite low expression in leaf and undetectable in root [30]. In addition, TaCAD12 in response to R. cerealis infection through comparative transcriptomics was isolated. TaCAD12 is a gene to improve wheat resistance to sharp eyespot representing the roles in plant defense responses [38].

Thirteen IbCADs were isolated from EST library of the sweetpotato (Ipomoea batatas) suspension culture. They were classified Group I to IV, according to sequence homology. Group I (IbCAD1-IbCAD6), group II (IbCAD7-IbCAD11), group III (IbCAD12), and group IV (IbCAD13) showed different structural characteristics and different expression patterns. IbCAD gene family under environmental stresses represented diverse expression, which could be useful for tolerance to stresses [21]. It may be involved in the lignin biosynthesis induced by both abiotic and biotic stresses and in tis-sue-specific developmental lignification through a CAD gene family network.

Multiple CAD isoforms described above were differentially expressed during plant development and environmental stresses. They may have substrate preferences, and this makes it possible to determine the lignin type to synthesize. According to several reports, chemical composition of defense lignin and developmental lignin was different. Substrate-specific induction of CAD was affected to its function in regulating the composition of lignin types. It was shown that G lignin was apparently presented to defense response in wounded poplar and almond tree, while G-S developmental lignin was found in these species [14]. In wounded wheat tissues, the content of S lignin was increased and sinapyl alcohol dehydrogenase activity was induced [27]. These inconsistent results in relation to the monomer composition of between developmental and defense lignin assumed a complex control of monolignol biosynthesis under external stimulation.

CAD gene family have different functions, such as, one isoform could be associated with the developmental lignification, whereas others are related defense lignins and wall-bound phenolics. The CAD isoforms indicated comparable catalytic activities with coniferaldehyde and sinapaldehyde. Different functional and biochemical characteristics of CAD proteins have been considered to the different isoforms identified in various plants [21,40].

Transcriptional regulation by CAD promoter

To identify potential mechanisms controlling CAD gene expression, expression of CAD promoter was represented. CAD has been purified from the xylem tissues in Eucalyptus, and the corresponding mRNA was highly expressed. The activity of EgCAD2 promoter was high in cells undergoing lignification, such as vasculature, root tip and emerging lateral root [26]. Whereas, EgCAD1 promoter was active in other cells and tissues which were not lignified. In such cells, CAD activity is likely to be associated with monolignol production for non-lignin. OsCAD2 promoter in rice was expressed in vascular tissues in aerial parts of the plant, which is correlated with lignification [15]. The GUS expression of each AtCAD promoter revealed complex patterns, including both temporal and spatial regulation during growth and development. AtCAD4 and AtCAD5 were primarily involved in the lignin formation of the xylem tissues. The expression pattern of AtCAD1, AtCAD6, and AtCAD9 showed similar to AtCAD4 and AtCAD5. Especially, AtCAD9 is involved in developmental lignification in the primary xylem of stems. On the other hands, AtCAD7 and AtCAD8 might not be associated with developmental lignification. AtCAD2 and AtCAD3 also are involved in other biosynthetic pathway because they had no GUS expression pattern specific to the vascular system [8,19]. Sweetpotato IbCAD1 promoter expression was strong in the roots. Weak GUS expression was observed in lignified tissues of vascular system of mature leaves and stems. IbCAD1 promoter activity was strongly induced in response to the biotic and abiotic stresses [20].

In conclusion, genetic regulation of CAD multigene family is complex and the signal pathway is overlapping. Synthesis of monolignol by CAD genes is likely to be regulated by development and environmental cues as well (Fig. 2).

SMGHBM_2021_v31n10_944_f0002.png 이미지

Fig. 2. Overlapping signal pathway for development and defense-related regulation of CAD gene.

The Conflict of Interest Statement

The authors declare that they have no conflicts of interest with the contents of this article.

References

  1. Barakat, A., Bagniewska-Zadmorna, A., Choi, A., Plakkat, U., Diloreto, D. S., Yellanki, P. and Carlson, J. E. 2009. The cinnamyl alcohol dehydrogenase gene family in Populus: phylogeny, organization and expression. BMC Plant Biol. 9, 26. https://doi.org/10.1186/1471-2229-9-26
  2. Baucher, M., Bernard-Vailhe, M. A., Chabbert, B., Besle, J. M., Opsomer, C., Montagu, M. V. and Botterman, J. 1999. Down-regulation of cinnamyl alcohol dehydrogenase in transgenic alfafa (Medicago sativa L.) and the effect on lignin composition and digestibility. Plant Mol. Biol. 39, 437-447. https://doi.org/10.1023/A:1006182925584
  3. Boerjan, W., Ralph, J. and Bouncher, M. 2003. Lignin biosynthesis. Annu. Rev. Plant Biol. 54, 519-546. https://doi.org/10.1146/annurev.arplant.54.031902.134938
  4. Boudet, A. M., Lapierre, C. and Grima-Pettenati, J. 1995. Biochemistry and molecular biology of lignification. New Phytol. 129, 203-236. https://doi.org/10.1111/j.1469-8137.1995.tb04292.x
  5. Brill, E. M., Abrahams, S., Hayes, C. M., Jenkins, C. L. D. and Watson, J. M. 1999. Molecular characterization and expression of a wound-inducible cDNA encoding a novel cinnamyl alcohol dehydrogenase enzyme in lucerne (Medicago sativa L.). Plant Mol. Biol. 41, 279-291. https://doi.org/10.1023/A:1006381630494
  6. Campbell, M. M. and Ellis, B. E. 1992. Fungal elicitor-mediated responses in pine cell cultures. Planta 186, 409-417. https://doi.org/10.1007/BF00195322
  7. Chen, L., Auh, C. K., Dowling, P., Bell, J., Chen, F., Hopkins, A., Dixon, R. A. and Wang, Z. Y. 2003. Improved forage digestibility of tall fescue (Festuca arundinacea) by transgenic down-regulation of cinnamyl alcohol dehydrogenase. Plant Biotechnol. J. 1, 437-449. https://doi.org/10.1046/j.1467-7652.2003.00040.x
  8. Eudes, A., Pollet, B., Sibout, R., Do, C. T., Seguin, A., Lapierre, C. and Jouanin, L. 2006. Evidence for a role of AtCAD1 in lignification of elongating stems of Arabidopsis thaliana. Planta 225, 23-39. https://doi.org/10.1007/s00425-006-0326-9
  9. Goffner, D., Joffroy, I., Grima-Pettenati, J., Halpin, C., Knight, M. E., Schuch, W. and Boudet, A. M. 1992. Purification and characterization of isoforms of cinnamyl alcohol dehydrogenase from Eucalyptus xylem. Planta 188, 48-53. https://doi.org/10.1007/BF00198938
  10. Grima-Petterniati, J., Feuillet, C., Goffner, D., Borderies, G. and Boudet, A. M. 1993. Molecular cloning and expression of a Eucalpytus gunnii cDNA clone encoding cinnamyl alcohol dehydrogenase. Plant Mol. Biol. 221, 1085-1095.
  11. Guillaumie, S., San-Clemente, H., Deswarte, C., Martinez, Y., Lapierre, C., Murigneux, A., Barriere, Y., Pichon, M. and Goffner, D. 2007. MAIZEWALL. Database and developmental gene expression profiling of cell wall biosynthesis and assembly in maize. Plant Physiol. 143, 339-363. https://doi.org/10.1104/pp.106.086405
  12. Halpin, C., Knight, M. E., Foxon, G. A., Campbell, M. M., Boudet, A. M., Boon, J. J., Chabbert, B., Tollier, M. and Schuch, W. 1994. Manipulation of lignin quality by down-regulation of cinnamyl alcohol dehydrogenase. Plant J. 6, 339-350. https://doi.org/10.1046/j.1365-313X.1994.06030339.x
  13. Halpin, C., Holt, K., Chojecki, J., Oliver, D., Chabbert, B., Monties, B., Edewards, K., Barakate, A. and Foxon, G. A. 1998. Brown-midrib maize (bm1): a mutation affecting the cinnamyl alcohol dehydrogenase gene. Plant J. 14, 545-553. https://doi.org/10.1046/j.1365-313X.1998.00153.x
  14. Hawkins, S. W. and Boudet, A. M. 2003. 'Defense lignin' and hydroxycinnamyl alcohol dehydrogenase activities in wounded Eucalyptus gunnii. For. Path. 33, 91-104. https://doi.org/10.1046/j.1439-0329.2003.00308.x
  15. Hirano, K., Aya, K., Kondo, M., Okuno, A., Morinaka, Y. and Matsuoka, M. 2012. OsCAD2 is the major CAD gene responsible for monolignol biosynthesis in rice culm. Plant Cell Rep. 31, 91-101. https://doi.org/10.1007/s00299-011-1142-7
  16. Jin, Y., Zhang, C., Liu, W. and Qi, H. 2014. The cinnamyl alcohol dehydrogenase gene family in melon (Cucumis melo L.): bioinformatic analysis and expression patterns. PLoS One 9, 7.
  17. Kiedrowski, S., Kawalleck, P., Hahlbrock, K., Somssich, I. E. and Dangl, E. 1992. Rapid activation of a novel plant defense gene is strictly dependent on the Arabidopsis RPM1 disease resistance locus. EMBO J. 11, 4677-4684. https://doi.org/10.1002/j.1460-2075.1992.tb05572.x
  18. Kim, S. J., Kim, M. R., Bedgar, K. L., Moinuddin, S. G. A., Cardenas, C. L., Davin, L. B., Kang, C. and Lewis, N. G. 2004. Functional reclassification of the putative cinnamyl alcohol dehydrogenase multigene family in Arabidopsis. Proc. Natl. Acad. Sci. USA. 101, 1455-1460. https://doi.org/10.1073/pnas.0307987100
  19. Kim, S. J., Kim, K. W., Cho, M. H., Franceschi, V. R., Davin, L. B. and Lewis, N. G. 2007. Expression of cinnamyl alcohol dehydrogenases and their putative homologues during Arabidopsis thaliana growth and development: Lessons for database annotations? Phytochemistry 68, 1957-1974. https://doi.org/10.1016/j.phytochem.2007.02.032
  20. Kim, Y. H., Bae, J. M. and Huh, G. H. 2010. Transcriptional regulation of the cinnamyl alcohol dehydrogenase gene from sweetpotato in response to plant developmental stage and environmental stress. Plant Cell Rep. 29, 779-791. https://doi.org/10.1007/s00299-010-0864-2
  21. Kim, Y. H. and Huh, G. H. 2019a. Molecular characterization and expression of the cinnamyl alcohol dehydrogenase gene family in sweetpotato (Ipomoea batatas) under environmental stresses. Hortic. Sci. Technol. 37, 279-289. https://doi.org/10.7235/HORT.20190027
  22. Kim, Y. H. and Huh, G. H. 2019b. Overexpression of cinnamyl alcohol dehydrogenase gene from sweetpotato enhances oxidative stress tolerance in transgenic Arabidopsis. In Vitro Cell Dev. Biol. Plant 55, 172-179. https://doi.org/10.1007/s11627-018-09951-5
  23. Lacombe, E., Van Doorsselaere, J., Boerjan, W., Boudet, A. M. and Grima-Pettenati, J. 2000. Characterization of cis-elements required for vascular expression of the cinnamoyl-CoA reductase gene and for protein-DNA complex formation. Plant J. 23, 663-676. https://doi.org/10.1046/j.1365-313x.2000.00838.x
  24. Lange, B. M., Lapierre, C. and Sandermann, H. Jr. 1995. Elicitor-induced spruce stress lignin: Structural similarity to early developmental lignins. Plant Physiol. 108, 1277-1287. https://doi.org/10.1104/pp.108.3.1277
  25. Lauvergeat, V., Lacomme, C., Lacombe, E., Lasserre, E., Roby, D. and Grima-Petterniati, J. 2001. Two cinnamoylCoA reductase (CCR) genes from Arabidopsis thaliana are differentially expressed during development and in response to infection with pathogenic bacteria. Phytochemistry 57, 1187-1195. https://doi.org/10.1016/S0031-9422(01)00053-X
  26. Lauvergeat, V., Rech, P., Jauneau, A., Guez, C., Coutos-Thevenot, P. and Grima-Pettenati, J. 2002. The vascular expression pattern directed by the Eucalyptus gunnii cinnamyl alcohol dehydrogenase EgCAD2 promoter is conserved among woody and herbaceous plant species. Plant Mol. Biol. 50, 497-509. https://doi.org/10.1023/A:1019817913604
  27. Li, L., Cheng, X. F., Leshkevich, J., Umezawa, T., Harding, S. A. and Chiang, V. L. 2001. The last step of syringyl monolignol biosynthesis in angiosperm is regulated by a novel gene encoding sinapyl alcohol dehydrogenase. Plant Cell 13, 1567-1585. https://doi.org/10.2307/3871387
  28. Li, X., Yang, Y., Yao, J., Chen, G., Li, X., Zhang, Q. and Wu, C. 2009. FLEXIBLE CULM1 encoding a cinnamyl alcohol dehydrogenase controls culm mechanical strength in rice. Plant Mol. Biol. 69, 685-697. https://doi.org/10.1007/s11103-008-9448-8
  29. Lynch, D., Lidgett, A., Mclnnes, R., Huxley, H., Jones, E., Mahoney, N. and Spangenberg, G. 2002. Isolation and characterization of three cinnamyl alcohol dehydrogenase homologue cDNAs from perennial ryegrass (Lolium perenne L.). J. Plant Physiol. 159, 653-660. https://doi.org/10.1078/0176-1617-0776
  30. Ma, Q. H. 2010. Functional analysis of a cinnamyl alcohol dehydrogenase involved in lignin biosynthesis in wheat. J. Exp. Bot. 61, 2735-2744. https://doi.org/10.1093/jxb/erq107
  31. Ma, D., Xu, C., Alejos-Gonzalez, F., Wang, H., Yang, J., Judd, R. and Xie, D. Y. 2018. Overexpression of Artemisia annua cinnamyl alcohol dehydrogenase increases lignin and coumarin and reduces artemisinin and other sesquiterpenes. Front. Plant Sci. 9, 828. https://doi.org/10.3389/fpls.2018.00828
  32. MacKay, J. J., Liu, W., Whetten, R., Sederoff, R. R. and O'Malley, D. M. 1995. Genetic analysis of cinnamyl alcohol dehydrogenase in loblolly pine: Single gene inheritance, molecular characterization and evolution. Mol. Gen. Genet. 247, 537-545. https://doi.org/10.1007/BF00290344
  33. MacKay, J. J., O'Malley, D. M., Presnell, T., Booker, F. L., Campbell, M. M., Whetten, R. W. and Sederoff, R. R. 1997. Inheritance, gene expression, and lignin characterization in a mutant pine deficient in cinnamyl alcohol dehydrogenase. Proc. Natl. Acad. Sci. USA. 94, 8255-8260. https://doi.org/10.1073/pnas.94.15.8255
  34. Mitchell, H. J., Hall, J. L. and Barber, M. S. 1994. Elicitor-induced cinnamyl alcohol dehydrogenase activity in lignifying wheat (Triticum aestivum L.) leaves. Plant Physiol. 104, 551-556. https://doi.org/10.1104/pp.104.2.551
  35. Mclnnes, R., Lidgett, A., Lynch, D., Huxley, H., Jones, E., Mahoney, N. and Spangenberg, G. 2002. Isolation and characterization of a cinnamoyl-CoA reductase gene from perennial ryegrass (Lolium perenne). J. Plant Physiol. 159, 415-422. https://doi.org/10.1078/0176-1617-00719
  36. Park, H. L., Kim, T. L., Bhoo, S. H., Lee, T. H., Lee, S. W. and Cho, M. H. 2018. Biochemical characterization of the rice cinnamyl alcohol dehydrogenase gene family. Molecules 23, 2659. https://doi.org/10.3390/molecules23102659
  37. Pichon, M., Courbou, I., Bechert, M., Boudet, A. M. and Grima-Pettenati, J. 1998. Cloning and characterization of two maize cDNAs encoding cinnamoyl CoA reductase (CCR) and differential expression of the corresponding genes. Plant Mol. Bol. 38, 671-676. https://doi.org/10.1023/A:1006060101866
  38. Rong, W., Luo, M., Shan, T., Wei, X., Du, L., Xu, H. and Zhang, Z. 2016. A wheat cinnamyl alcohol dehydrogenase TaCAD12 contributes to host resistance to the sharp eyespot disease. Front. Plant Sci. 7, 1723.
  39. Saballos, A., Ejeta, G., Sanchez, E., Kang, C. and Vermerris, W. 2009. A genome-wide analysis of the cinnamyl alcohol dehydrogenase family in sorghum (Sorghum bicolor (L.) Moench) identities SbCAD2 as the Brown midrib6 gene. Genetics 181, 783-795. https://doi.org/10.1534/genetics.108.098996
  40. Somers, D. A., Nourse, J. P., Manners, J. M., Abrahams, S. and Watson, J. M. 1995. A gene encoding a cinnamyl alcohol dehydrogenase homolog in Arabidopsis thaliana. Plant Physiol. 108, 1309-1310. https://doi.org/10.1104/pp.108.3.1309
  41. Somssich, I. E., Wernert, P., Kiedrowski, S. and Hahlbrock, K. 1996. Arabidopsis thaliana defense-related ELI3 is an aromatic alcohol:NADP+ oxidoreductase. Proc. Natl. Acad. Sci. USA. 93, 14199-14203. https://doi.org/10.1073/pnas.93.24.14199
  42. Sibout, R., Eudes, A., Mouille, G., Pollet, B., Lapierre, C., Jouanin, L. and Seguin, A. 2005. Cinnamyl alcohol dehydrogenase-C and -D are the primary genes involved in lignin biosynthesis in the floral stem of Arabidopsis. Plant Cell 17, 2059-2076. https://doi.org/10.1105/tpc.105.030767
  43. Tobias, C. M. and Chow, E. K. 2005. Structure of the cinnamyl alcohol dehydrogenase gene family in rice and promoter activity of a member associated with lignification. Planta 220, 678-688. https://doi.org/10.1007/s00425-004-1385-4
  44. Whetten, R. and Sederoff, R. 1995. Lignin biosynthesis. Plant Cell 7, 1001-1013. https://doi.org/10.1105/tpc.7.7.1001
  45. Yoon, J., Choi, H. and An, G. 2015. Roles of lignin biosynthesis and regulatory genes in plant development. J. Integr. Plant Biol. 57, 902-912. https://doi.org/10.1111/jipb.12422
  46. Zhang, K., Qian, Q., Huang, Z., Wang, Y., Li, M., Hong, L., Zeng, D., Gu, M., Chu, C. and Cheng, Z. 2006. GOLD HULL AND INTERNODE2 encodes a primarily multifunctional cinnamyl alcohol dehydrogenase in rice. Plant Physiol. 140, 972-983. https://doi.org/10.1104/pp.105.073007