Study On The Transcriptome And Proteome Of Rice Adapting To High Temperature At Early Milky Stage

Originating from low latitude areas, rice can survive certain high temperatures, but its normal growth will be impaired once the temperature is higher than the threshold of its growth-optimal temperature. Unfortunately, it is highly likely that crops will have to adjust to even higher temperatures in the near future because of global climate change. In China, high-temperature damage happens mainly in the zone of double-cropping early-season rice at Yangtze River Valley and some areas to its south from early to middle July, because the ridge line of western pacific subtropical anticyclone located these areas at the period, which cause long hot weather in the middle and lower reaches of Yangtze River. This period happens to be the early grain-filling stage of double-cropping early-season rice in the area around the Yangtze River Valley, which often results in low grain quantity and yield loss. Double-cropping early-season rice is an important and irreplaceable food crop in southern China. Therefore, strengthening the researches on molecular mechanisms of heat tolerant characteristic in rice as well as breeding rice cultivars with heat tolerant characteristic at grain-filling stage plays a significant role in maintaining rice yield stability and guaranteeing the human food security.In our previous work, a recombinant inbred line (RIL) related to heat-tolerance at rice grain-filling stage and derived from Xieqingzao B/N22were inbred. In present study,791rice lines of the RIL were used as plant materials;1. The heat-tolerant and physiological characteristics of rice at grain-filling stage were determined and the genomic polymorphism were analyzed by SSR molecular markers, among the791RILs;2. The physiological indexes of flag leaves related to photosynthesis, oxidation of cell membrane and osmotic adjustment were analyzed and compared between treatment and control of both XN0437S and XN0437T rice lines;3. differentially expressed genes related to heat-tolerant characteristic of rice caryopsis were analyzed and compared between treatment and control of both XN0437S and XN0437T rice lines by cDNA-AFLP;4. differentially expressed proteins related to heat-tolerant characteristic of rice caryopsis were analyzed and compared between treatment and control of both XN0437S and XN0437T rice lines by proteomics based on two-dimensional electrophoresis (2-DE). The results are as follow.1. Two rice lines. XN0437T (heat-tolerant) and XN0437S (heat-sensitive) with similar genome but significant difference in heat-tolerant trait at grain-filling stage, were obtained from the791RILs.2. Chlorophyll content and photosynthesis rate of rice flag leaves were decreased, while the matters content of cell membrane oxidation and permeability of plasma membrane were increased, under high temperature stress, which resulted in a change of intracellular environment, but the influence of the heat sensitive rice was more severe than that of the heat tolerant rice.3. Fifty-four differentially expressed gene fragments from rice caryopsis were obtained by cDNA-AFLP. Among them,27genes had homologous genes in the GenBank database and another27gene fragments were newly identified. Further analysis with RT-PCR indicated that genes involved in adverse stress were showed up-regulation and the up-regulated degree in the heat-tolerant rice line XN0437T was higher than that of the heat-sensitive rice line XN0437S, while the other up-regulated genes were involved in metabolism, transcription, biosynthesis and oxidation, and the up-regulated degree of the heat-tolerant rice line XN0437T was lower than that of the heat-sensitive rice line XN0437S. Genes involved in transcription, biosynthesis, photosynthesis, methylation and substance transportation were down-regulated, and the down-regulated degree in the heat-sensitive rice line XN0437T was higher than that of the heat-tolerant rice line XN0437S.4. Twenty-three differentially expressed proteins from rice caryopsis were obtained after a proteomics study, but only9proteins had homologous proteins in the protein database of Matrixscience. Functions of the homologous proteins included oxidation, biosynthesis, gene transcription, phosphorylation and starch synthesis. Proteins involved in oxidation and biosynthesis showed up-regulation, while proteins involved in transcription, phosphorylation and starch synthesis showed down-regulation. There are12and2unknown proteins that showed up and down regulation respectively under high temperature stress.The research results indicated that physiological cause of rice plumpness decrease was that photo synthetic products and storage matters transported to plumpness were reduced, due to the decrease of photosynthesis rate and the increase of cell membrane oxidation and permeability of plasma membrane. Molecular biological cause of rice plumpness decreased was that genes involved in biosynthesis of storage products, and genes involved in transcription, phosphorylation and starch biosynthesis were down-regulated, while that genes involved in adverse stress and proteins encoded by genes involved in oxidation and biosynthesis were up-regulated.The54candidate genes and23candidate proteins identified in the present study will be helpful for elucidating the molecular mechanism on rice adapting high temperature stress.