Plant Sciences, University of California, Davis, CA 95616, USA.
Phytopathology. 2012 Feb;102(2):222-8. doi: 10.1094/PHYTO-03-11-0075.
Broadening of the genetic base for identification and transfer of genes for resistance to insect pests and diseases from wild relatives of rice is an important strategy in resistance breeding programs across the world. An accession of Oryza nivara, International Rice Germplasm Collection (IRGC) accession number 105710, was identified to exhibit high level and broad-spectrum resistance to Xanthomonas oryzae pv. oryzae. In order to study the genetics of resistance and to tag and map the resistance gene or genes present in IRGC 105710, it was crossed with the bacterial blight (BB)-susceptible varieties 'TN1' and 'Samba Mahsuri' (SM) and then backcrossed to generate backcross mapping populations. Analysis of these populations and their progeny testing revealed that a single dominant gene controls resistance in IRGC 105710. The BC(1)F(2) population derived from the cross IRGC 105710/TN1//TN1 was screened with a set of 72 polymorphic simple-sequence repeat (SSR) markers distributed across the rice genome and the resistance gene was coarse mapped on chromosome 7 between the SSR markers RM5711 and RM6728 at a genetic distance of 17.0 and 19.3 centimorgans (cM), respectively. After analysis involving 49 SSR markers located between the genomic interval spanned by RM5711 and RM6728, and BC(2)F(2) population consisting of 2,011 individuals derived from the cross IRGC 105710/TN1//TN1, the gene was fine mapped between two SSR markers (RMWR7.1 and RMWR7.6) located at a genetic distance of 0.9 and 1.2 cM, respectively, from the gene and flanking it. The linkage distances were validated in a BC(1)F(2) mapping population derived from the cross IRGC 105710/SM//2 × SM. The BB resistance gene present in the O. nivara accession was identified to be novel based on its unique map location on chromosome 7 and wider spectrum of BB resistance; this gene has been named Xa33. The genomic region between the two closely flanking SSR markers was in silico analyzed for putatively expressed candidate genes. In total, eight genes were identified in the region and a putative gene encoding serinethreonine kinase appears to be a candidate for the Xa33 gene.
拓宽遗传基础，以便从水稻野生近缘种中鉴定和转移抗虫和抗病基因，是全球抗性育种计划的一项重要策略。国际水稻种质资源（IRGC）登录号为 105710 的野生稻 Oryza nivara 品系，被鉴定为对稻黄单胞菌 pv.oryzae 具有高水平和广谱的抗性。为了研究抗性的遗传基础，并对 IRGC 105710 中存在的抗性基因进行标记和作图，将其与细菌性条斑病（BB）感病品种“TN1”和“Samba Mahsuri”（SM）杂交，然后回交产生回交作图群体。对这些群体及其后代的分析表明，一个单一的显性基因控制着 IRGC 105710 的抗性。从 IRGC 105710/TN1//TN1 杂交中衍生的 BC(1)F(2)群体，用一组分布在整个水稻基因组中的 72 个多态性简单序列重复（SSR）标记进行筛选，抗性基因被粗略地定位在 RM5711 和 RM6728 两个 SSR 标记之间的第 7 号染色体上，遗传距离分别为 17.0 和 19.3 厘摩（cM）。在涉及位于 RM5711 和 RM6728 基因组区间内的 49 个 SSR 标记和由 IRGC 105710/TN1//TN1 杂交衍生的包含 2011 个个体的 BC(2)F(2)群体的分析之后，该基因被精细地定位在位于基因两侧的两个 SSR 标记（RMWR7.1 和 RMWR7.6）之间，遗传距离分别为 0.9 和 1.2 cM。该连锁距离在由 IRGC 105710/SM//2 × SM 杂交衍生的 BC(1)F(2)作图群体中得到了验证。在第 7 号染色体上的独特图谱位置和更广泛的 BB 抗性基础上，确定 O. nivara 品系中存在的 BB 抗性基因是新的，该基因被命名为 Xa33。在两个紧密连锁的 SSR 标记之间的基因组区域进行了候选基因的计算机分析。在该区域共鉴定出 8 个基因，其中一个编码丝氨酸-苏氨酸激酶的基因似乎是 Xa33 基因的候选基因。
