Beecher B, Murfett J, McClure B A
Department of Biochemistry, University of Missouri-Columbia 65211, USA.
Plant Mol Biol. 1998 Mar;36(4):553-63. doi: 10.1023/a:1005904230755.
Unilateral incompatibility often occurs between self-incompatible (SI) species and their self-compatible (SC) relatives. For example, SI Nicotiana alata rejects pollen from SC N. plumbaginifolia, but the reciprocal pollination is compatible. This interspecific pollen rejection system closely resembles intraspecific S-allele-specific pollen rejection. However, the two systems differ in degree of specificity. In SI, rejection is S-allele-specific, meaning that only a single S-RNase causes rejection of pollen with a specific S genotype. Rejection of N. plumbaginifolia pollen is less specific, occurring in response to almost any S-RNase. Here, we have tested whether a non-S-RNase can cause rejection of N. plumbaginifolia pollen. The Escherichia coli rna gene encoding RNAseI was engineered for expression in transgenic (N. plumbaginifolia x SC N. alata) hybrids. Expression levels and pollination behavior of hybrids expressing E. coli RNaseI were compared to controls expressing SA2-RNase from N. alata. Immunoblot analysis and RNase activity assays showed that RNaseI and SA2-RNase were expressed at comparable levels. However, expression of SA2-RNase caused rejection of N. plumbaginifolia pollen, whereas expression of RNaseI did not. Thus, in this system, RNase activity alone is not sufficient for rejection of N. plumbaginifolia pollen. The results suggest that S-RNases may be specially adapted to function in pollen rejection.
单侧不亲和性经常发生在自交不亲和（SI）物种与其自交亲和（SC）的近缘物种之间。例如，自交不亲和的烟草（Nicotiana alata）会排斥来自自交亲和的垂花烟草（N. plumbaginifolia）的花粉，但反过来授粉却是亲和的。这种种间花粉排斥系统与种内S等位基因特异性花粉排斥非常相似。然而，这两种系统在特异性程度上有所不同。在自交不亲和中，排斥是S等位基因特异性的，这意味着只有单一的S-RNase会导致具有特定S基因型的花粉被排斥。垂花烟草花粉的排斥特异性较低，几乎对任何S-RNase都会产生反应。在此，我们测试了一种非S-RNase是否会导致垂花烟草花粉被排斥。编码核糖核酸酶I的大肠杆菌rna基因经过改造，以便在转基因（垂花烟草×自交亲和的烟草）杂种中表达。将表达大肠杆菌核糖核酸酶I的杂种的表达水平和授粉行为与表达来自烟草的SA2-RNase的对照进行了比较。免疫印迹分析和核糖核酸酶活性测定表明，核糖核酸酶I和SA2-RNase的表达水平相当。然而，SA2-RNase的表达导致垂花烟草花粉被排斥，而核糖核酸酶I的表达则没有。因此，在这个系统中，仅核糖核酸酶活性不足以导致垂花烟草花粉被排斥。结果表明，S-RNases可能经过特殊适应而在花粉排斥中发挥作用。
