Murfett J., Strabala T. J., Zurek D. M., Mou B., Beecher B., McClure B. A.
University of Missouri-Columbia, Department of Biochemistry, 117 Schweitzer Hall, Columbia, Missouri 65211.
Plant Cell. 1996 Jun;8(6):943-958. doi: 10.1105/tpc.8.6.943.
In self-incompatible (SI) plants, the S locus acts to prevent growth of self-pollen and thus promotes outcrossing within the species. Interspecific crosses between SI and self-compatible (SC) species often show unilateral incompatibility that follows the SI x SC rule: SI species reject pollen from SC species, but the reciprocal crosses are usually compatible. The general validity of the SI x SC rule suggests a link between SI and interspecific pollen rejection; however, this link has been questioned because of a number of exceptions to the rule. To clarify the role of the S locus in interspecific pollen rejection, we transformed several Nicotiana species and hybrids with genes encoding SA2 or SC10 RNase from SI N. alata. Compatibility phenotypes in the transgenic plants were tested using pollen from three SC species showing unilateral incompatibility with N. alata. S RNase was implicated in rejecting pollen from all three species. Rejection of N. plumbaginifolia pollen was similar to S allele-specific pollen rejection, showing a requirement for both S RNase and other genetic factors from N. alata. In contrast, S RNase-dependent rejection of N. glutinosa and N. tabacum pollen proceeded without these additional factors. N. alata also rejects pollen from the latter two species through an S RNase-independent mechanism. Our results implicate the S locus in all three systems, but it is clear that multiple mechanisms contribute to interspecific pollen rejection.
在自交不亲和（SI）植物中，S位点阻止自花花粉生长，从而促进物种内异花授粉。SI物种和自交亲和（SC）物种之间的种间杂交通常表现出遵循SI×SC规则的单向不亲和性：SI物种排斥SC物种的花粉，但反交通常是亲和的。SI×SC规则的普遍有效性表明SI与种间花粉排斥之间存在联系；然而，由于该规则存在一些例外情况，这种联系受到了质疑。为了阐明S位点在种间花粉排斥中的作用，我们用来自SI烟草（N. alata）的编码SA2或SC10核糖核酸酶的基因转化了几种烟草属物种及其杂种。使用来自三种与烟草表现出单向不亲和性的SC物种的花粉，对转基因植物的亲和表型进行了测试。S核糖核酸酶参与了对所有这三个物种花粉的排斥。对蓝烟草（N. plumbaginifolia）花粉的排斥类似于S等位基因特异性花粉排斥，表明既需要S核糖核酸酶，也需要烟草的其他遗传因子。相比之下，对黏烟草（N. glutinosa）和烟草花粉的S核糖核酸酶依赖性排斥在没有这些额外因子的情况下也能进行。烟草还通过一种不依赖S核糖核酸酶的机制排斥后两个物种的花粉。我们的结果表明S位点参与了所有这三个系统，但很明显，多种机制导致了种间花粉排斥。
