Screening And Identification Of NILs For Drought Resistance QTL And Differential Responsive Genes In Rice

As the world population continues to expand, food shortages will become increasingly severe. Rice (Oryza sativa) is one of the most important crops and is a staple food for a large segment of the world population. Therefore, continuing to increase rice yield is vital to relieving the growing pressure for greater food production. Because of the reduction of available water resources and frequent unexpected meteorological events, such as absence or uneven distribution of rainfall, drought stress is becoming one of the major limiting factors for rice production. Understanding the mechanisms underlying yield formation and drought resistance is crucial for breeding rice varieties with greater yield potential and drought resistance.In this study,38 drought resistance-related QTL were selected to develop near-isogenic lines (NILs) and phenotypic variations of 17 NILs for drought resistance-related QTL were investigated under drought and normal conditions. One NIL showing increased rice root volume, flag leaf width, and spikelet number per panicle was identified and fine mapping was performed for the corresponding QTL. The main results are as follow:Comparisons of the changes in morphological physiological respones and the gene expression profiles between two parents, Zhenshan 97 (ZS97) and IRAT109, revealed that drought avoidance is the main drought resistance mechanism of IRAT109 that has stronger water absorbing and retaining capacity, such as larger root system, faster leaves rolling, and lower rate of water loss. The response of IRAT109 to drought was earlier at the gene expression level. For ZS97, drought tolerance is the main drought resistance mechanism and the capacity of osmotic adjustment is stronger, such as better maintenance of ion balance and cell membrane stability.Thirty-eight drought resistance-related QTL were selected to develop NILs from previous research result. So far,9 NILs at BC6F1 generation,23 NILs at BC4F2 generation, and 34 NILs at BC3F1 generation for drought resistance have been generated. Phenotypic variations of 17 NILs for drought resistance-related QTL were investigated under drought and normal conditions. Fourteen of these NILs showed significant phenotypic differences relative to the recurrent parent under at least one of the conditions and nine NILs showed significant differences under both conditions. After eliminating the effect of heading date on drought resistance, only four QTL intervals for the same grain yield-related traits and three QTL intervals for the same or similar root traits showed differences consistent with the original QTL mapping results.By checking the expression patterns of 36 drought-responsive genes (located in 14 QTL intervals with the NILs showing significant phenotypic difference) in ZS97, IRAT109, and near isogenic lines of the QTL intervals, we found that more than half of the genes had their expression patterns or expression levels changed in the near isogenic lines under normal and/or drought conditions when compared to that in ZS97 or IRAT109.Using a population containing approximately 12,000 plants, a QTL (designed as qFSR4) controlling root volume and co-segregating with flag leaf width and spikelet number per panicle was mapped to a 38-kb region containing 3 putative genes by bioinformatics predicting including the previously characterized NARROW LEAF1 (NAL1) gene. The genomic sequence and expression level of NAL1 show significant differences between ZS97 and IRAT109, so NAL1 may be the most promising candidate gene for these three traits.Based on the gene expression profiles of IRAT109 and ZS97 under drought conditions,30 constructs were made for 15 candidate genes for drought resistance and genetic transformation and expression analysis of them were finished. The responses to stress resistance for part transgenic plants were tested. Over-expression transgenic rice for G11, encoding a putatice cyclase, showed increased sensitivity to drought and salt stress.Systematic sequence analyses were performed for BURP family since most of the genes in this family are responsive to drought stress. Expression level analysis of 17 BURP genes of rice under different stress conditions and in various tissues and organs revealed that transcript levels of 14 BURP genes were responsive to different stress conditions including drought, salt, cold and ABA stress,5 BURP genes were predominantly expressed in panicle and 5 BURP genes were predominantly expressed in seedling before tillering stage.