Septiningsih Endang M, Pamplona Alvaro M, Sanchez Darlene L, Neeraja Chirravuri N, Vergara Georgina V, Heuer Sigrid, Ismail Abdelbagi M, Mackill David J
International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Ann Bot. 2009 Jan;103(2):151-60. doi: 10.1093/aob/mcn206. Epub 2008 Oct 30.
Submergence is a recurring problem in the rice-producing rainfed lowlands of south and south-east Asia. Developing rice cultivars with tolerance of submergence and with agronomic and quality traits acceptable to farmers is a feasible approach to address this problem. The objectives of this study were to (a) develop mega varieties with Sub1 introgression that are submergence tolerant, (b) assess the performance of Sub1 in different genetic backgrounds, (c) determine the roles of the Sub1A and Sub1C genes in conferring tolerance, and (d) assess the level of tolerance in F(1) hybrids heterozygous for the Sub1A-1-tolerant allele.
Tolerant varieties were developed by marker-assisted backcrossing through two or three backcrosses, and their performance was evaluated to determine the effect of Sub1 in different genetic backgrounds. The roles of Sub1A and Sub1C in conferring the tolerant phenotype were further investigated using recombinants identified within the Sub1 gene cluster based on survival and gene expression data.
All mega varieties with Sub1 introgression had a significantly higher survival rate than the original parents. An intolerant Sub1C allele combined with the tolerant Sub1A-1 allele did not significantly reduce the level of tolerance, and the Sub1C-1 expression appeared to be independent of the Sub1A allele; however, even when Sub1C-1 expression is completely turned off in the presence of Sub1A-2, plants remained intolerant. Survival rates and Sub1A expression were significantly lower in heterozygotes compared with the homozygous tolerant parent.
Sub1 provided a substantial enhancement in the level of tolerance of all the sensitive mega varieties. Sub1A is confirmed as the primary contributor to tolerance, while Sub1C alleles do not seem important. Lack of dominance of Sub1 suggests that the Sub1A-1 allele should be carried by both parents for developing tolerant rice hybrids.
淹水是南亚和东南亚雨养低地水稻产区反复出现的问题。培育具有耐淹性且具备农民可接受的农艺性状和品质性状的水稻品种是解决这一问题的可行途径。本研究的目标是：（a）培育导入Sub1基因的耐淹巨型品种；（b）评估Sub1在不同遗传背景下的表现；（c）确定Sub1A和Sub1C基因在赋予耐受性方面的作用；（d）评估携带Sub1A - 1耐淹等位基因的F1杂种的耐受水平。
通过标记辅助回交两到三次培育耐淹品种，并评估其表现以确定Sub1在不同遗传背景下的作用。基于存活和基因表达数据，利用在Sub1基因簇内鉴定出的重组体进一步研究Sub1A和Sub1C在赋予耐受表型方面的作用。
所有导入Sub1基因的巨型品种的存活率均显著高于其原始亲本。不耐淹的Sub1C等位基因与耐淹的Sub1A - 1等位基因组合并不会显著降低耐受水平，且Sub1C - 1的表达似乎独立于Sub1A等位基因；然而，即使在存在Sub1A - 2的情况下Sub1C - 1的表达完全关闭，植株仍不耐淹。与纯合耐淹亲本相比，杂合子的存活率和Sub1A表达显著较低。
Sub1显著提高了所有敏感巨型品种的耐受水平。Sub1A被确认为耐受性的主要贡献者，而Sub1C等位基因似乎并不重要。Sub1缺乏显性表明，为培育耐淹水稻杂种，双亲都应携带Sub1A - 1等位基因。
