• Molecules and Cells
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• v.40 no.1
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• pp.17-23
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• 2017

Mitogen-activated protein kinase (MAPK) signaling cascades play critical roles in various cellular events in plants, including stress responses, innate immunity, hormone signaling, and cell specificity. MAPK-mediated stress signaling is also known to negatively regulate nitrogen-fixing symbiotic interactions, but the molecular mechanism of the MAPK signaling cascades underlying the symbiotic nodule development remains largely unknown. We show that the MtMKK5-MtMPK3/6 signaling module negatively regulates the early symbiotic nodule formation, probably upstream of ERN1 (ERF Required for Nodulation 1) and NSP1 (Nod factor Signaling Pathway 1) in Medicago truncatula. The overexpression of MtMKK5 stimulated stress and defense signaling pathways but also reduced nodule formation in M. truncatula roots. Conversely, a MAPK specific inhibitor, U0126, enhanced nodule formation and the expression of an early nodulation marker gene, MtNIN. We found that MtMKK5 directly activates MtMPK3/6 by phosphorylating the TEY motif within the activation loop and that the MtMPK3/6 proteins physically interact with the early nodulation-related transcription factors ERN1 and NSP1. These data suggest that the stress signaling-mediated MtMKK5/MtMPK3/6 module suppresses symbiotic nodule development via the action of early nodulation transcription factors.

• Korean Journal of Plant Resources
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• v.10 no.3
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• pp.250-257
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• 1997

The relationship of nine Medicago species belonging to four subgenera were analyzed by using SDS-PAGE and restriction fragment length polymorphism (RELP) methodologies. Sixty-eight bands of alcohol and salt soluble proteins and 85-133 RFLP markers were used to estimate the genetic distance among the species. These species were clustered together at around 0.1 to 0.4 level of distance for both kind of markers, indicating that Medicago species have a large genetic similarity. A combined cluster diagram, at a dissimilarity level of 0.3, differentiated nine species in four groups: group 1, M. littoralis , M. truncatulam, M.scutellata and M. rigidula; group 2, M. sativa ; group 3, M. lupulina ; group 4, M. orbicularis, M. radiata and M. minima. All of them, but except for M. minima. corrensponded to the existing four subgenera of the genus Medicago classified by Lesins and Lesins(1979).The most similar species were M. littoralis and M. trucatula and the most dissimilar one was M. lupulina. In separate cluster diagrams based on RFLP and protein markers, some differences were observed. In the case of RFLP or DNA markers, M. sativa (alfalfa) was distantly clustered with other Medicago species. But in the case of protein markers, M. sativa was closely clustered with M. scutellata, M. littorulis and M. truncatula.

• Journal of Applied Biological Chemistry
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• v.44 no.3
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• pp.125-130
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• 2001

A putative protein encoded by Arabidopsis AtMTN3 gene, a homologue of Medicago truncatula MTN3, consists of 285 amino acid residues, and has a predicted molecular mass of 31.5 kDa and a calculated pI of 9.1. Primary amino acid sequence analyses have revealed that the protein contains seven putative transmembrane regions with N-terminus oriented to the outside of the membrane. The AtMTN3 protein shows overall 16.4% of amino acid identity with the rat GALR3 protein, known to be a G-protein-coupled receptor. The gene is present as a single copy in the Arabidopsis genome, and expressed in aerial parts but not in roots of Arabidopsis. Therefore, AtMTN3 appears not to be specifically involved in Rhizobium-induced nodule development, as was predicted for the MTN3 gene. These proteins possibly mediate signal transmission through G-protein-coupled pathways during general interactions between plants and symbiotic or pathogenic microbes.

• The Plant Pathology Journal
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• v.20 no.1
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• pp.18-21
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• 2004

The root hair provides a major entering spot for the symbiotic legume rhizobia. It is obvious that dynamic cell wall modification occurs in the plant root hair during the early microbe invasion. Expansins are nondestructive cell wall-modifying proteins that are involved in cell growth and differentiation. Among about 40 expansin genes in Arabidopsis, two expansin genes are expressed specifically in the root hair cell. Orthologous genes of this Arabidopsis root hair expansins have been found in other Brassica members, rice, and Medicago truncatula (a legume). In this review, I discuss the probable function of expansins during the early symbiotic process between the root hair and microbes and the regulation of root hair expansin genes in a comparative approach.