National Maize Improvement Center, China Agricultural University, Beijing 100193, China.
J Genet Genomics. 2010 Jan;37(1):57-68. doi: 10.1016/S1673-8527(09)60025-4.
The rice indica/japonica hybrid shows strong heterosis. However, such inter-subspecific hybrid can't be directly used in rice production due to its low spikelet fertility. The S5 locus was proved to be associated with fertility of indica/japonica hybrid and its S5n allele from wide-compatibility variety (WCV) is capable to overcome fertility barrier. In the present study, we reported the causal sites in the S5 locus responsible for compatibility of indica/japonica hybrid. Fine-mapping of the S5 locus using the 11 test-cross families pinpoints a candidate S5 locus encoding aspartic protease (Asp). Intragenic recombination within the Asp gene happened in a number of recombinants, resulting in chimeric S5j-S5n alleles. Just like S5n, the chimeric S5j-S5n allele displayed higher spikelet fertility when combined with the S5i allele. In the complementary test, however, the S5n allele from WCVs failed to enhance fertilities of the indica/japonica hybrids. Compared to both indica and japonica varieties, all nine WCVs from different resources are characterized with a 136 bp deletion in the Asp N-terminus, which probably renders the S5n allele non-functional. Furthermore, an A/C polymorphic site is detected 1,233 bp downstream of the Asp start codon. The heterozygous A/C site of the Asp gene in indica/japonica hybrid is believed to be the casual factor to cause partial sterility. The functional makers based on the two polymorphic sites will be broadly used in developing wide-compatibility rice varieties.
籼稻/粳稻杂种表现出很强的杂种优势。然而，由于其小穗育性低，这种亚种间杂种不能直接用于水稻生产。已经证明 S5 位点与籼稻/粳稻杂种的育性有关，其来自广亲和品种（WCV）的 S5n 等位基因能够克服育性障碍。在本研究中，我们报道了导致籼稻/粳稻杂种亲和性的 S5 位点的候选基因。利用 11 个测交家系对 S5 位点进行精细定位，确定了一个与 S5 位点相关的候选基因，该基因编码天冬氨酸蛋白酶（Asp）。在一些重组体中，Asp 基因内发生了基因内重组，导致了嵌合 S5j-S5n 等位基因。与 S5n 一样，嵌合 S5j-S5n 等位基因与 S5i 等位基因结合时，表现出更高的小穗育性。然而，在互补试验中，WCV 中的 S5n 等位基因未能提高籼稻/粳稻杂种的育性。与籼稻和粳稻品种相比，来自不同资源的 9 个 WCV 均在 Asp N 端缺失 136 bp，这可能使 S5n 等位基因失去功能。此外，在 Asp 起始密码子下游 1233 bp 处检测到一个 A/C 多态性位点。在籼稻/粳稻杂种中，Asp 基因的杂合 A/C 位点被认为是导致部分不育的原因。基于这两个多态性位点的功能标记将广泛用于开发广亲和水稻品种。
