Murfett J, Atherton T L, Mou B, Gasser C S, McClure B A
Department of Biochemistry, University of Missouri-Columbia 65211.
Nature. 1994 Feb 10;367(6463):563-6. doi: 10.1038/367563a0.
Many angiosperms employ self-incompatibility systems to prevent inbreeding. The simple genetics of such systems have made them attractive models of plant cellular communication. Implicit in the single locus genetics is that only one or a few gene products are necessary for recognition and rejection of incompatible pollen. Results in the sporophytic system of the Brassicaceae suggest that different S-locus products are responsible for the pollen and pistil parts of the recognition and rejection response. In solanaeceous plants, which have a gametophytic self-incompatibility system, the S locus product responsible for the pollen portion of the interaction has not been identified, but ribonucleases encoded by the S-locus (S-RNases) are strongly implicated in the style part of the recognition and rejection reaction. In Nicotiana alata, pollen recognition and rejection occur if its S-allele matches either S-allele in the style. The putative stylar S-RNase is abundant in the transmitting tract, and pollen rejection may be related to action of S-RNase on pollen RNAs. Efforts to understand the molecular basis for pollen recognition and rejection have been limited by the lack of a system for manipulating and expressing S-RNases. Here we use the promoter of a style-expressed gene from tomato to obtain high levels of S-RNase expression in transgenic Nicotiana. Recognition and rejection of N. alata pollen S-alleles occur faithfully in the transgenic plants. Our results show that S-RNases alone are sufficient for pollen rejection in this system.
许多被子植物利用自交不亲和系统来防止近亲繁殖。这类系统简单的遗传学特性使其成为植物细胞通讯的诱人模型。单基因座遗传学中隐含的观点是，识别和排斥不亲和花粉仅需一种或少数几种基因产物。十字花科植物孢子体系统的研究结果表明，不同的S基因座产物分别负责识别和排斥反应中的花粉和雌蕊部分。在具有配子体自交不亲和系统的茄科植物中，负责花粉相互作用部分的S基因座产物尚未确定，但S基因座编码的核糖核酸酶（S-RNases）被强烈认为与识别和排斥反应的花柱部分有关。在烟草中，如果其S等位基因与花柱中的任何一个S等位基因匹配，就会发生花粉识别和排斥。假定的花柱S-RNase在花粉管通道中大量存在，花粉排斥可能与S-RNase对花粉RNA的作用有关。由于缺乏操纵和表达S-RNases的系统，了解花粉识别和排斥分子基础的努力受到了限制。在这里，我们利用番茄中一个花柱表达基因的启动子，在转基因烟草中获得了高水平的S-RNase表达。转基因植物中能如实地发生对烟草花粉S等位基因的识别和排斥。我们的结果表明，在这个系统中，仅S-RNases就足以导致花粉排斥。
