Recent Advances in the Studies of Self-Incompatibility of plants

식물의 자가불화합성, 최근의 진보

Many flowering plants possess genetically controlled self -incompatibility (SI) system that prevents inbreeding and promotes outcrosses. SI is usually controlled by a single, multiallelic S-locus. In gametophytically controlled system, SI results when the S-allele of the pollen is matched by one of the two S-alleles in the style, while in the sporophytic system self-incompatible reaction occurs by the interaction between the pistil genotype and genotype of, not the pollen, but the pollen parent In the former system the self-incompatible phenotype of pollen is determined by the haploid genome of the pollen itself but in the latter the pollen phenotype is governed by the genotype of the pollen parent along with the occurrence of either to-dominant or dominant/recessive allelic interactions. In the sporophytic type the inhibition reaction occurs within minutes following pollen-stigma contact, the incompatible pollen grains usually failing to germinate, whereas in gametophytic system pollen tube inhibition takes place during growth in the transmitting tissue of the style. Recognition and rejection of self pollen are the result of interaction between the S-locus protein in the pistil and the pollen protein. In the gametophytic SI the S-associated glycoprotein which is similar to the fungal ribonuclease in structure and function are localized at the intercellular matrix in the transmitting tissue of the style, with the highest concentration in the collar of the stigma, while in the sporophytic SI deposit of abundant S-locus specific glycoprotein (SLSG).is detected in the cell wall of stigmatic papillae of the open flowers. In the gametophytic system S-gene is expressed mostly at the stigmatic collar the upper third of the style length and in the pollen after meiosis. On the other hand, in the sporophytic SI S-glycoprotein gene is expressed in the papillar cells of the stigma as well as in e sporophytic tape is cells of anther wall. Recognition and rejection of self pollen in the gametophytic type is the reaction between the ribonuclease in the transmitting tissue of the style and the protein in the cytoplasm of pollen tube, whereas in the sporophytic system the inhibition of selfed pollen is caused by the interaction between the Sycoprotein in the wall of stigmatic papillar cell and the tapetum-origin protein deposited on the outer wall of the pollen grain. The claim that the S-allele-associated proteins are involved in recognition and rejection of self pollen has been made merely based on indirect evidence. Recently it has been verified that inhibition of synthesis of S$_3$ protein in Petunia inflata plants of S$_2$S$_3$ genotype by the antisense S$_3$ gene resulted in failure of the transgenic plant to reject S$_3$ pollen and that expression of the transgenic encoding S$_3$ protein in the S$_1$S$_2$ genotype confers on the transgenic plant the ability to reject S$_3$ pollen. These finding Provide direct evidence that S-proteins control the s elf-incompatibility behavior of the pistil.