Characterization Of Aquaporin Genes In Tomato During Drought Stress And Fruit Development Process

Tomato(Solanum lycopersicum) is one of the most popular cultivation fruit of the world. Water is necessary during tomato plant growth, fruit development and fruit postharvest process. Aquaporin gene as a kind of special water transport channel, involved in water plant moisture absorption and transport ion in plant. This study was to explore the the role of tomato aquaporins in response to drought stress, fruit development and fruit postharvest process.1. The function of aquaporin (AQP) protein in transporting water is crucial for plants to survive in drought stress. With47homologues in tomato (Solarium lycopersicum) were reported, but the individual and integrated functions of aquaporins involved in drought response remains uncleare. Here, three plasma membrane intrinsic protein genes, SIPIP2;1, SIPIP2;7and SIPIP2;5, were identified as candidate aquaporins genes because of highly expressed in tomato roots. GFP fluorescent microscopy indicated that all of the three proteins were localized to the plasma membrane. Assay on expression in Xenopus oocytes demonstrated that SIPIP2s protein displayed water channel activity and facilitated water transport into the cells. With real-time PCR and in situ hybridization analysis, SIPIP2s were considered to be involved in response to drought treatment. To test its function, transgenic Arabidopsis and tomato lines overexpressing SIPIP2;1, SIPIP2;7or SIPIP2;5were generated.Compared with wild type, the over-expression of SIPIP2;1, SIPIP2;7or SIPIP2;5transgenic Arabidopsis plants showed significantly higher hydraulic conductivity levels and survival rates under both normal and drought conditions. The transgenic tomato lines had lower levels of malondialdehyde (MDA), but higher relative water content(RWC) when compared with the wild type (WT) under drought stress. Taken together, this study concludes that aquaporins (SIPIP2;1, SIPIP2;7and SIPIP2;5) contribute substantially to root water uptake in tomato plants through improving plant water content and maintaining osmotic balance.2. The expression of11PIPs and9TIPs aquaporin genes was detected during fruit development using real-time PCR. The expression of SIPIP2;5, SIPIP1;4, SIPIP2;7, SIPIP2;1, SIPIP2;8, SIPIP2;4, SlTIP1;5and SlTIP1;4were upregulated during the early fruit development stages. While the expression of SlTIP1;1, SITIP, SITIP1;3were upregulated during later fruit development stages. Exogenous auxin treatment shown that the expression of aquaporin genes were siginificant regulated, especially for SIPIP2;4which upregulated9.4times. Compare to wild type fruit, overexpression SIPIP2;4transgenic fruit shown higher fresh weight, but there were no siginificant different in fruit dry weight. This result explained that SIPIP2;4were regulated by auxin, involving in water accumulation. 3. In order to explore the role of tomato aquaporins during fruit postharvest storage process, the expression of11PIPs and9TIPs aquaporin genes were detected under ethylene or1-methyl propylene (1-MCP) treatment. We identified a aquaporin gene, SlPIP1;4, which were shown a downregulation espression after ethylene treatment while shown a upregulation after1-MCP treatment. The expression of SlPIP1;4was downregulated in SlETRs-silenced fruit. Compared to control fruit, the loss of water in SlPIP1;4-silenced fruit were faster, suggested that SlPIP1;4played an important role through maintaining water balance during fruit storage.