Drought Resistance Evaluation、Gene Discovery And Study On Drought Tolerance Mechanism In Rice

Rice(Oryza sativa L.)is one of the most important crops,as the staple food for more than half of the world’s population.Rice has poor drought resistance and rice production accounts for nearly half of the total consumption of freshwater.Caused by global warming,extreme weather environments,i.e.drought and high temperature imposed a great threat to rice production.Breeding of water-saving and drought resistant rice is a valuable solution responding to food and water crisis.Remarkable progresses have been achieved in researching and genetic improvement of drought resistance in rice including finding of drought resistance genes and release of drought resistant varieties.Nevertheless,our understanding is still very limited to the genetic mechanism of drought resistance as a complex quantitative trait with multiple strategies.Two different methods were used in this study.Firstly,genome-wide association study was conducted in core collection of rice germplasm to explore QTLs and candidate genes for drought resistance.Secondly,transcriptomic and metabolomic analysis was used to explore drought tolerant mechanism in rice.The main findings are as follows:1.Based on the phenotypic data of 270 rice germplasm accessions,plant height,biomass,yield per plant,panicle length,number of primary branches,number of secondary branches,seed setting rate,number of spikelets per spike,leaf length and leaf width were significantly suppressed by drought stress.Heading date was significantly delayed while chlorophyll content(SPAD value)increased after drought stress.2.Fourteen rice varieties with good comprehensive drought resistance and two rice varieties with poor comprehensive drought resistance were identified by soil moisture drought resistance identification systems,barrel test method and "basket" experiment respectively.Six varieties were grouped to drought-avoidance,three varieties to drought-tolerance,one to drought recovery.Two japonica rice varieties have both drought tolerance and drought avoidance.Two indica varieties have drought tolerance,drought avoidance and drought recovery.Although the comprehensive drought resistance and drought avoidance are very close between IAC1246 and IRAT109,the drought tolerance of IAC1246 is significantly stronger than IRAT109.Thus,IAC1246 can be used as a donor parent in study and breeding of drought tolerance in rice.3.Association mapping in this study detected genomic regions hosting many function-known genes for plant height and drought resistance,including sd1,GH3-2, Os GA2ox3,Os SAP11/Os DOG,Os GNA1,Os CYP51G3,Os RRMh,Os PYL2,and Os GA2ox9.Twenty-eight candidate genes for drought resistance were found in the association interval of drought resistance coefficient.In this study,one of the candidate genes,Os RLK5 was knocked out by CRISPR/Cas9 in Nipponbare.Compared to the wild type,the mutant lines showed faster water loss and significant lower seed setting rate and yield-related traits under drought conditions.4.Compared with IRAT109,IAC1246 have a stronger osmotic adjustment ability and antioxidant capacity and fewer dead leaves under drought stress condition.That can finally produce a higher yield and reflect the strong drought tolerance in IAC1246.Transcriptomic analysis showed that the number of DEGs in IRAT109 was more than in IAC1246,and only fewer DEGs were commonly detected.KEGG enrichment analysis showed that DEGs were significantly enriched in glucose metabolism and amino acid metabolism pathway in IRAT109 during the severe drought stress,and DEGs were significantly enriched in antioxidant-related pathways in IAC1246,including glutathione metabolism,anabolic flavones and flavonoids,ascorbic acid metabolism,antioxidant carotenoids.GO enrichment analysis showed that DEGs can be significantly enriched in water channel activity in IRAT109 during different periods,but not in IAC1246 at any time.These results indicate that IAC1246 depend on improving antioxidant capacity,while IRAT109 depend on water transport to response to drought stress.5.Most photosynthesis-related DEGs displayed different regulatory patterns between IRAT109 and IAC1246,particularly at period I.Many of these DEGs were up-regulated in IAC1246,while they were down-regulated in IRAT109.The chloroplast genes in IRAT109 and IAC1246 exhibited a similar pattern of regulation compared to the photosynthesis-related DEGs.6.Metabolomic analysis showed more differential metabolites were detected in IRAT109 than in IAC1246.Nine differential metabolites were common detected.Some same differential metabolites showed different expression patterns.The contents of ferulic acid and 4-hydroxycinnamic acid were greatly increased in IAC1246 at drought period I,while they were only slightly increased in IRAT109 at the same period.