Transcription Factor OsbZIP5 Negatively Regulates Drought-tolerance in Rice / 中国生物化学与分子生物学报

ABSTRACT

Drought is a major abiotic stress factor which affects the growth and yield of rice (Oryza sativa) and other crops seriously. Cloning and identifying drought-tolerant genes and exploring the drought-tolerant mechanism are of great significance for improving grain yield. In this paper, a bZIP family transcription factor encoding gene, OsbZIP5, was cloned from rice and we conducted a preliminary study on its drought tolerance function. We constructed different expression plasmids, including p35SOsbZIP5-GFP4, pGBKT7-OsbZIP5, pCAMBIA1300-OsbZIP5-OE and pTCK303-OsbZIP5-RNAi, which were transformed into tobacco, yeast, Arabidopsis or rice, respectively. Confocal observation of OsbZIP5-GFP4 transgenic tobacco showed that OsbZIP5 was located in the nucleus. The reporter gene expression analysis of pGBKT7-OsbZIP5 transformed yeast showed that the protein can activate the expression of reporter genes and OsbZIP5 has transcription activational activity. The drought tolerance of OsbZIP5 overexpression transgenic Arabidopsis during the seedling and reproductive growth stages was analyzed, and the results showed that OsbZIP5 overexpression reduced the root length of seedlings under polyethyleneglycol (PEG) or abscisic acid (ABA) treatment and the drought tolerance of adult plants in transgenic Arabidopsis. The drought tolerance and stress tolerance related physiological parameters were tested using 20% PEG to simulate drought stress. It was found that the survival rates of different OsbZIP5 RNAi transgenic rice lines were 65%, 58. 30%, and 73. 30%, respectively, while that of the wild type was 21. 67%. Under normal growth conditions, the content of proline, chlorophyll and malondialdehyde in RNAi transgenic rice are basically the same as those of wild type. However, after PEG treatment, the average values of the parameters above of RNAi transgenic rice were 159. 54 μg/ g FW, 0. 24 mg/ g FW and 7. 44 nmol/ g FW, respectively, while the average value of the wild type were 102. 56 μg/ g FW, 0. 13 mg/ g FW and 13. 61 nmol/ g FW, respectively. Statistical analysis of stomata and water loss rate under drought treatment of rice leaves revealed that the proportions of fully closed stomata of all OsbZIP5 RNAi lines were above 66% while that of the wild type is about 50%. And the water loss rate of rice leaves in RNAi rice seedlings were lower than that of wild type. We showed that down-regulation of OsbZIP5 ameliorated the physiological parameters, reduced stomata opening and water loss rate, and improved the drought tolerance of RNAi transgenic rice. The results above suggested that OsbZIP5 was a negative regulator of drought stress tolerance in rice.