Kumar Pawan, He Yajun, Singh Rippy, Davis Richard F, Guo Hui, Paterson Andrew H, Peterson Daniel G, Shen Xinlian, Nichols Robert L, Chee Peng W
Cotton Molecular Breeding Laboratory, University of Georgia, Tifton, GA, 31793, USA.
Present Address: College of Agronomy and Biotechnology, Southwest University, Chongqing, 400716, China.
BMC Genomics. 2016 Aug 8;17:567. doi: 10.1186/s12864-016-2954-1.
The southern root-knot nematode (Meloidogyne incognita; RKN) is one of the most important economic pests of Upland cotton (Gossypium hirsutum L.). Host plant resistance, the ability of a plant to suppress nematode reproduction, is the most economical, practical, and environmentally sound method to provide protection against this subterranean pest. The resistant line Auburn 623RNR and a number of elite breeding lines derived from it remain the most important source of root-knot nematode (RKN) resistance. Prior genetic analysis has identified two epistatically interacting RKN resistance QTLs, qMi-C11 and qMi-C14, affecting gall formation and RKN reproduction, respectively.
We developed a genetic population segregating only for the qMi-C14 locus and evaluated the genetic effects of this QTL on RKN resistance in the absence of the qMi-C11 locus. The qMi-C14 locus had a LOD score of 12 and accounted for 24.5 % of total phenotypic variation for egg production. In addition to not being significantly associated with gall formation, this locus had a lower main effect on RKN reproduction than found in our previous study, which lends further support to evidence of epistasis with qMi-C11 in imparting RKN resistance in the Auburn 623RNR source. The locus qMi-C14 was fine-mapped with the addition of 16 newly developed markers. By using the reference genome sequence of G. raimondii, we identified 20 candidate genes encoding disease resistance protein homologs in the newly defined 2.3 Mb region flanked by two SSR markers. Resequencing of an RKN resistant and susceptible G. hirsutum germplasm revealed non-synonymous mutations in only four of the coding regions of candidate genes, and these four genes are consequently of high interest.
Our mapping results validated the effects of the qMi-C14 resistance locus, delimiting the QTL to a smaller region, and identified tightly linked SSR markers to improve the efficiency of marker-assisted selection. The candidate genes identified warrant functional studies that will help in identifying and characterizing the actual qMi-C14 defense gene(s) against root-knot nematodes.
南方根结线虫（Meloidogyne incognita；RKN）是陆地棉（Gossypium hirsutum L.）最重要的经济害虫之一。寄主植物抗性，即植物抑制线虫繁殖的能力，是抵御这种地下害虫最经济、实用且环保的方法。抗性品系奥本623RNR及其衍生的一些优良育种品系仍然是根结线虫（RKN）抗性的最重要来源。先前的遗传分析已鉴定出两个上位性相互作用的RKN抗性QTL，即qMi-C11和qMi-C14，分别影响根瘤形成和RKN繁殖。
我们构建了仅在qMi-C14位点分离的遗传群体，并在不存在qMi-C11位点的情况下评估了该QTL对RKN抗性的遗传效应。qMi-C14位点的LOD值为12，占产卵量总表型变异的24.5%。除了与根瘤形成无显著关联外，该位点对RKN繁殖的主效应比我们先前的研究中发现的要低，这进一步支持了在奥本623RNR品系中qMi-C11与qMi-C14之间存在上位性互作赋予RKN抗性的证据。通过添加16个新开发的标记对qMi-C14位点进行了精细定位。利用雷蒙德氏棉（G. raimondii）的参考基因组序列，我们在两个SSR标记侧翼新定义的2.3 Mb区域内鉴定出20个编码抗病蛋白同源物的候选基因。对RKN抗性和感病的陆地棉种质进行重测序发现，仅在四个候选基因的编码区存在非同义突变，因此这四个基因备受关注。
我们的定位结果验证了qMi-C14抗性位点的效应，将该QTL定位到一个更小的区域，并鉴定出紧密连锁的SSR标记以提高标记辅助选择的效率。所鉴定的候选基因值得进行功能研究，这将有助于鉴定和表征实际的抗根结线虫qMi-C14防御基因。
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