Effect Of Drought Stress During Panicle Differentiation Stage On The Grain Size And GS3 Gene Expression In Rice

Abiotic stresses(drought, flood, high or low temperature and salinity etc.) greatly reduce yields for most major crops by more than 50% every year. Drought is a major factor limiting crop production worldwide, about 45% of the world agricultural lands are subject to continuous or frequent drought each year. Rice is particularly sensitive to drought stress during reproductive growth, when drought stress can result in shrinking of panicle and grain size and thus lead to drastic reduction in grain yield. Many studies on mechanisms under drought stress have been based on gene expression. QRT-PCR is currently the most widely used method to detect the transcript of interest gene.In this study, rice variety Chuanxian 955 and 9311 were used as experimental materials. And we established and optimized the reaction conditions of real-time PCR. The method of detecting the interest gene expression under drought stress by real-time PCR was established using the most stable house keeping genes screened out as the internal control. The expression of GS3 gene (controlling grain length and width) was studied under drought stress during reproductive growth. The main results were as follows:1. The variation of rice grain size of different varieties under drought stressGrain size of two rice varieties shrinked at different degrees under drought stress during panicle differentiation stage. The values of grain length, width and 1000-grain weight decreased significantly (p≤0.01) while the length-width ratio remained unchanged in Chuanxian 955. However, except for a significant decrease in grain length (significant at p= 0.05), the changes of other traits related to grain size were not significant in 9311.2. Differential expression of GS3 gene at different stages of panicle initiation under drought stressFor the rice variety Chuanxian955, The expression levels of gene GS3 under drought stress were slightly lower than that of the control in early stages of panicle development (3-6d after panicle initiation). At 11d after panicle initiation (spikelet primordium differentiation stage), however, there was a sharp increase of GS3 expression under drought stress, the maximum expression level increased up to 4.8-fold compared with that of the control. The GS3 expression under drought stress leveled up in later stages but remained higher than that of the control till 18d after panicle initiation. For the variety 9311, the gene expression of GS3 during different stages showed a similar pattern though the differences between the drought stressed materials and the control were smaller as compared with Chuanxian955. The shrinking of grain size under drought stress could be attributed to the over expression of GS3 which is a negative regulator for grain size.3. Expression stability of the housekeeping genesRelatively stable housekeeping genes should be used as as the internal control for detecting the differential expression of an interest gene under different conditions by real-time PCR. The expression stability of 10 the housekeeping genes (8 paralogous genes for actin, together with eEF-1a and b-tub) were studied under drought stress. With analysis of the geNorm program, the most stable genes were ACT(X16280)1 and eEF-1a. The M value obtained for both genes was 0.384. The screened housekeeping genes ACT(X16280)1 and eEF-1a could be used as reliable internal controls for studying the expression of other target genes under drought stress in rice.