Cloning Of DREB Gene From Rice And Effect Of Drought On Rice Quality

Drought, low temperature and high salt are adverse abiotic environment that greatly affected the growth of plant and the productivity and quality of crops.DREB transcription factor can specifically interact with the dehydration-responsive element/C-repeat (DRE/CRT) cis-acting element that was reported in the promoter region of many stress-inducible genes and control the expression of many stress-inducible genes in plant, and so increase tolerance to drought, low temperature and high salt.In this paper we cloned a novel DREB gene, and studied the effect of drought on rice quality. The results are showed as below.1. Primers were designed according to high homology in the conserved regions of the amino acid sequences of DREB protein, amplified them by PCR, and cloned a novel DREB-like gene. We named it B02 gene. It contains an open reading frame (ORF) of 1218 nucleotides, and encodes 405 amino acids. The putative amino acid sequence has a predicted molecular mass of 44 kDa and a pI of 4.6. There is no intron in the ORF of genomic gene. It contains the typical characteristics to DREB transcription factor, the protein rich basic amino acid in its N-terminal region that potentially served as a nuclear localization signal and an acidic C-terminal region that might act as a transcriptional activation domain. 58 amino acids constitute a conserved regions DNA binding protein domain in its middle region, the 14th and 19th amino acids site are valine and glutamic acid, respectively.Searching the rice 9311-genome database with BLAST program, we discovered B02 gene was located at chromosome 5. We found that B02 had high homology with several DREB2 in plant, for example, 67% identity to DREB-like proteingene (AY646223) from indica rice, 67% and 64% identity to DREB2A (AB007790) and DREB2B (AB007791) from Arabidopsis, respectively, 64% identity to OsDREB2A (AF300971) from japonica rice, 58% identity to DREB2G and 52% identity to DREB2C from Arabidopsis.Base on the amino acids sequences of AP2 domain of DREB protein and VAEIRE amino acids sequences between V14 and E19. Comparing the B02 to other DREB proteins from rice and Arabidopsis, we get a DREB molecular evolution tree, and found the B02 gene belonged to DREB2, so renamed it DREB2-like gene. Therefore we may predict that it possibly has a function of DREB2, the expression patterns of the B02 gene might be induced by drought, high salt and ABA.2. Using 9 hybrid combinations and 4 restorer lines, the effect of continuous drought on rice quality, was analyzed during flowering, filling and seed-setting stages. The results showed that the drought reduced milling quality of rice, especially, most significantly decreased the head rice rate. The drought treatment also increased chalky grain rate and chalkiness significantly, but the effect on grain shape was not very significant. These results indicated that the drought reduced grain appearance quality. In our experiments, because the drought raised gelatinization temperature, harden gel consistency and decrease amylose content of rice, cooking and eating quality of rice should be influenced. So, it was proposed that production of good quality rice should firstly select good quality variety, meanwhile, should choose production base with both of suitable temperature and sunlight condition and good irrigation condition. In the cultivation of quality rice, field water should be managed properly during filling and seed-setting stages, in which special attention should be paid to keep field suitable water (soil moisture) in the later stage.