Functional Analysis Of A Gene Involved In The Regulation Of Cold And Drought Stress Responses In Arabidopsis

With the completion of genome sequence of arabidopsis, rice and other model plants, plant scientists generally felt that its overall research focus should face to "functional genomics" research. Using gene expression microarray analysis data, expression of the LWT1 gene encoding a unkown protein was found to be induced by low temperature and drought stresses. However, it is unclear whether the LWT1 gene plays important roles in the regulation of the responses of Arabidopsis plants to low temperature and drought stresses.To elucidate the function of the LWT1 gene, two T-DNA insertion loss-of-function mutants lwt1-1 and lwt1-2 were obtained from the Arabidopsis Biological Resource Center. In this study, the responses of the lwt1-1 and lwt1-2 mutants to low temperature and drought stresses were investigated. The main results are as follows:1. Under low temperature stress, survival rates of the lwt1-1 and lwt1-2 mutant plants were lower than those of the wild type, and the electrolyte leakages of the lwt1-1 and lwt1-2 mutants were higher than the wild type, suggesting that the injury of the lwt1-1 and lwt1-2 mutants to low temperature stress in cellular level is more serious than to the wild type, and that the lwt1-1 and lwt1-2 mutants are more sensitive to low temperature stress than the wild type.2. Under drought stress, survival rates of the lwt1-1 and lwt1-2 mutant'plants were lower than those of the wild type, and the water loss rates of leaves in the lwt1-1 and lwt1-2 mutants were higher than the wild type, suggesting further evidence that mutant water-retention capacity is worse than wild-type and that the lwt1-1 and lwt1-2 mutants are more sensitive to drought stress than the wild type.3. Under low temperature and drought stress conditions, no significant difference in the level of soluble sugar was detected between the wild type and the lwtl-1 and lwtl-2 mutants, while a higher accumulation of proline was found in the wild type than in the lwt1-1 and lwt1-2 mutants, suggesting that the lwtl-1 and lwtl-2 mutants were sensitive to low temperature and drought, which is related to the accumulation of proline,not to the accumulation of soluble sugar.4. Analysis of expression of low temperature and drought stress-related genes showed that no significant difference in the pattern of CBFs gene expression was found between lwt1-1 and lwt1-2 mutants as well as the wild type, indicating that the sensitivity of the lwt1-1 and lwtl-2 mutants to low temperature and drought stresses was not related to CBFs signaling transduction pathway.5. Analysis of expression of proline synthesis-related gene P5CS and proline degradation-related gene PDH showed that the P5CS gene expression in the mutant lwt1-1 and lwt1-2 had no significant difference compared with the wild-type, while the PDH gene expression in lwt1-1 and lwt1-2 mutants was significantly higher than in the wild type, suggseting that LWT1 gene inhibited the expression of proline degradation gene, resulting in the accumulation of proline to low temperatures and drought stresses to adapt to the adverse environmental stresses.6. No significant differences in responses to mannitol, ABA, and NaCl treatments were found beween the lwt1-1 and lwt1-2 mutants and the wild-type. Our results suggusted that the intracellular accumulation of proline content which was regulated by LWT1 gene is the main reason for the sensitivity of lwt1-1 and lwtl-2 mutants to low temperature and drought stresses.In summary, the results provided evidence that LWT1 gene regulated plant responses to low temperature and drought stresses, mainly by controling the exprssion of proline degradation-related PDH gene.