Analyses of molecular genetic mechanism involved in the sporophytic self-incompatibility of Ipomoea.

自交不亲和性(SI)是一种阻止自交受精，从而促进异交以维持植物种群遗传多样性的遗传系统。在雌蕊识别自体和非自体花粉后，雌蕊通过拒绝自体花粉来工作。在旋花科植物中，有几种通菜具有孢子体类型的SI，该类型受单个多等位基因S控制。本研究旨在寻找与甘蓝自交花粉识别相关的S基因座，以揭示甘薯自交不亲和系统的分子机制。所取得的研究成果总结如下。(1)在S基因座附近构建了优良的遗传图谱。(2)采用基于图谱的定位克隆策略，从3个S单倍型的细菌人工染色体和粘粒文库中筛选出覆盖S基因座的基因组克隆。(3)序列分析表明，S基因座位于S单倍型特异的分歧区，大小在30~95kb之间。(4)Northern杂交和RT-PCR分析表明，3个柱头专化基因(SE1、SE2、SEA)和1个花药专化基因(AB2)分别编码雌蕊和花粉决定基因。(5)柱头特异基因的RNAi载体导入的转化体的SI表型没有发生变化，表明柱头特异基因可能具有互补功能。(6)本研究发现这些柱头特异的候选基因与已报道的其他植物的S基因没有同源性，这表明通子属植物的SI系统涉及一种独特的分子机制。

Self-incompatibility (SI) is a genetic system that prevents self-fertilization and thereby promotes out-crossing to maintain genetic diversity in plant populations. The SI system works through the rejection of self-pollen following the recognition of self and non-self pollen by the pistil. In the plant family, Convolvulaceae, several species of Ipomoea possess a sporophytic type of SI that is regulated by a single multiallelic S-locus. The present study was performed to identify the S-locus genes involved in the self-pollen recognition and to reveal molecular mechanism of the SI system in Ipomoea. Research results obtained are summarized as follows. (1) Fine genetic map of DNA markers was constructed in the vicinity of the S-locus. (2) Using a map-based positional cloning strategy, several genomic clones covering the S-locus were screened from bacterial artificial chromosome (BAC) and cosmid libraries of three S haplotypes. (3) Sequence analysis of the isolated clones showed that the S-loci were delimited to the S haplotype-specific divergent regions (SDRs) spanning 30 to 95 kb in size. (4) From gene expression analyses by Northern blot and RT-PCR of mRNAs, three stigma-specific genes (SE1, SE2, SEA) and an anther-specific gene (AB2) in the SDRs were identified as candidates encoding pistil and pollen determinants of the SI, respectively. (5) Transformants introduced with RNAi constructs of the stigma-specific genes showed no changes in the SI phenotypes, indicating that the stigma-specific genes might be functioned as complementary. (6) The present study revealed that these stigma specific candidates showed no homologies with the S-locus genes reported to date from other plants, and suggests that a unique molecular mechanism is involved in the SI system of Ipomoea plants.