Shiba H, Takayama S, Iwano M, Shimosato H, Funato M, Nakagawa T, Che F S, Suzuki G, Watanabe M, Hinata K, Isogai A
Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma 630-0101, Japan.
Plant Physiol. 2001 Apr;125(4):2095-103. doi: 10.1104/pp.125.4.2095.
Many flowering plants have evolved self-incompatibility (SI) systems to prevent inbreeding. In the Brassicaceae, SI is genetically controlled by a single polymorphic locus, termed the S-locus. Pollen rejection occurs when stigma and pollen share the same S-haplotype. Recognition of S-haplotype specificity has recently been shown to involve at least two S-locus genes, S-receptor kinase (SRK) and S-locus protein 11 or S-locus Cys-rich (SP11/SCR). SRK encodes a polymorphic membrane-spanning protein kinase, which is the sole female determinant of the S-haplotype specificity. SP11/SCR encodes a highly polymorphic Cys-rich small basic protein specifically expressed in the anther tapetum and in pollen. In cauliflower (B. oleracea), the gain-of-function approach has demonstrated that an allele of SP11/SCR encodes the male determinant of S-specificity. Here we examined the function of two alleles of SP11/SCR of B. rapa by the same approach and further established that SP11/SCR is the sole male determinant of SI in the genus Brassica sp. Our results also suggested that the 522-bp 5'-upstream region of the S9-SP11 gene used to drive the transgene contained all the regulatory elements required for the unique sporophytic/gametophytic expression observed for the native SP11 gene. Promoter deletion analyses suggested that the highly conserved 192-bp upstream region was sufficient for driving this unique expression. Furthermore, immunohistochemical analyses revealed that the protein product of the SP11 transgene was present in the tapetum and pollen, and that in pollen of late developmental stages, the SP11 protein was mainly localized in the pollen coat, a finding consistent with its expected biological role.
许多开花植物进化出了自交不亲和（SI）系统以防止近亲繁殖。在十字花科中，SI由一个单态性位点即S位点进行遗传控制。当柱头和花粉具有相同的S单倍型时，花粉会被排斥。最近研究表明，S单倍型特异性的识别至少涉及两个S位点基因，即S受体激酶（SRK）和S位点蛋白11或富含半胱氨酸的S位点蛋白（SP11/SCR）。SRK编码一种多态性跨膜蛋白激酶，它是S单倍型特异性的唯一雌性决定因子。SP11/SCR编码一种高度多态性的富含半胱氨酸的小碱性蛋白，该蛋白在花药绒毡层和花粉中特异性表达。在花椰菜（甘蓝变种）中，功能获得法已证明SP11/SCR的一个等位基因编码S特异性的雄性决定因子。在此，我们采用相同方法研究了白菜型油菜SP11/SCR的两个等位基因的功能，并进一步证实SP11/SCR是芸苔属植物SI的唯一雄性决定因子。我们的结果还表明，用于驱动转基因的S9-SP11基因522 bp的5'上游区域包含了天然SP11基因所观察到的独特孢子体/配子体表达所需的所有调控元件。启动子缺失分析表明，高度保守的192 bp上游区域足以驱动这种独特的表达。此外，免疫组织化学分析显示，SP11转基因的蛋白产物存在于绒毡层和花粉中，并且在发育后期的花粉中，SP11蛋白主要定位于花粉壁，这一发现与其预期的生物学作用一致。
