Evaluation Of Upland Rice Germplasm Resources And Screening Of Candidate Genes For Drought Resistance

Rice (Oryza sativa L.) is one of the most important cereal crops that provide the staple food for more than half of the world’s population. Water resources shortage is becoming more and more serious with global warming. The drought has become a severe problem that influences the rice yield. Therefore, evaluation of upland rice germplasm resources, identifying drought resistance related genes, and breeding drought resistant rice variety have been the major goal for our society.The study was conducted to analyze the genetic diversities and establish the DNA fingerprints of the upland rice in Henan Province by using SSR primers. Based on QTL mapping region related with root traits on chromosome 9, candidate genes controlling root traits and related to drought resistance were selected by predicting gene function from bioinformatics, analysis of difference of gene sequence and gene expression between upland rice and lowland rice, then the gene function was studied. The major research results are as followings.1. The genetic diversities of ten major upland rice cultivars in Henan was studied using 38 pairs of SSR primers, which equally distributed on 12 chromosomes of rice genome. The range of genetic similarity coefficient of the 10 varieties was from 0.435 to 0.907, with the average of 0.678. It is demonstrated that the genetic basis of upland rice is narrow in Henan. Ten cultivars could be identified through the core DNA fingerprints established using 7 highly polymorphic SSR primers (RM552, RM171, RM5, RM308, RM338, RM17, and RM587).2. Twenty genes that may be associated with drought-resistance were obtained from the QTL regions related to root drought-resistance through the sequencing information of rice genome and the references. There were two candidate genes, OsWRKY62 and OsbHLH120, screened through the DNA sequence alignment of twenty genes between lowland rice Yuefu, and upland rice IRAT109. The results of DNA sequence alignment of two candidate genes among 24 rice cultivars showed that OsbHLH120 had unique sequence in upland rice and the sequence diversity of which was significantly correlated with the basal root thickness and the root length.3. The expression of OsbHLH120 was induced by different stresses and depended on the ABA signal transduction. The expression of OsbHLH120 not obviously responsing to PEG stress was significantly increased in root of Yuefu treated with ABA and high salinity, but the expression in leaf was in a higher level after the PEG stress. However, the expression of OsbHLH120 allele was inducible in root of IRAT109 by all of the three stresses, especially the PGE and high salinity stress. From the above results, we can infere that OsbHLH120 is involved in the osmotic regulation and ion balance in leaf of lowland rice, and the specific allele OsbHLH120 of upland rice may participate in the osmotic regulation and ion balance in root to enhance the root drought resistance.4. Compared with the lowland rice, there are 15 bases deletion at downstream, 627-643bp, located at the transcription initiation codon of OsbHLH120 in the upland rice. Based on the sequence character, the functional marker, InDel-bHLH120, was designed. It can be used to screen and identifiy the upland rice germplasm containing the specific sequence of OsbHLH120 and used for the molecular marker-assistant selection of progeny segregation population.In conclusion, owing to the narrow genetic basis of the upland rice in Henan, various upland rice varieties should be introduced from different regions to expand the genetic diversity of breeding parents and to breed upland rice with high yield and strong drought tolerance. OsbHLH120 that related to the development of root can be induced by different stresses, which indicated that OsbHLH120 could be involved in osmotic regulation and ion balance regulation to enhance the drought avoidance and drought tolerance in upland rice. However, the specific allele OsbHLH120 in upland rice needs further research to understand its function in physiological regulation to enhance drought-resistant. The functional marker, InDel-bHLH120, can be used in the screening of upland rice germplasm and the molecular marker-assistant selection in rice drought resistance breeding.