Plasma Membrane Intrinsic Proteins SlPIP2;1, SlPIP2;7 and SlPIP2;5 Conferring Enhanced Drought Stress Tolerance in Tomato

Ren Li, Jinfang Wang, Shuangtao Li, Lei Zhang, Chuandong Qi, Sarah Weeda, Bing Zhao, Shuxin Ren, Yang-Dong Guo
2016 Scientific Reports  
The function of aquaporin (AQP) protein in transporting water is crucial for plants to survive in drought stress. With 47 homologues in tomato (Solanum lycopersicum) were reported, but the individual and integrated functions of aquaporins involved in drought response remains unclear. Here, three plasma membrane intrinsic protein genes, SlPIP2;1, SlPIP2;7 and SlPIP2;5, were identified as candidate aquaporins genes because of highly expressed in tomato roots. Assay on expression in Xenopus
more » ... demonstrated that SlPIP2s protein displayed water channel activity and facilitated water transport into the cells. With real-time PCR and in situ hybridization analysis, SlPIP2s were considered to be involved in response to drought treatment. To test its function, transgenic Arabidopsis and tomato lines overexpressing SlPIP2;1, SlPIP2;7 or SlPIP2;5 were generated. Compared with wild type, the over-expression of SlPIP2;1, SlPIP2;7 or SlPIP2;5 transgenic Arabidopsis and tomato plants all showed significantly higher hydraulic conductivity levels and survival rates under both normal and drought conditions. Taken together, this study concludes that aquaporins (SlPIP2;1, SlPIP2;7 and SlPIP2;5) contribute substantially to root water uptake in tomato plants through improving plant water content and maintaining osmotic balance. Water shortage is considered to be one of the most severe agricultural problems affecting plant growth 1 . In recent years, more attention has been paid to the possible role played by aquaporins in root water status and its relevance for defense mechanisms of plants against stress conditions. Previous studies have shown that there are three pathways to transport water: the apoplastic, symplastic and transcellular pathways 2 . Aquaporins (AQPs), which play a regulatory role in cellular water transport 3-6 , also called membrane protein family MIP (major intrinsic protein) 7-9 . There are 47 aquaporin genes in the tomato genome which can be divided into five different subfamilies based on subcellular localization and sequence homology: plasma membrane intrinsic proteins (PIPs), tonoplast intrinsic proteins (TIPs), NOD26-like MIPs or (NIPs), small basic intrinsic proteins (SIPs) 10,11 and the uncharacterized X intrinsic proteins (XIPs) 12 . Among PIPs, water channel activity is exhibited particularly by members of the PIP2 subgroup 13 . AQPs are considered the main channels for the transport of water along with small neutral solutes and CO 2 , through the plant cell membrane 9,14 . Hydraulic regulation determines the interplay between water potential gradients and waterflow intensity throughout the whole plant 15 . Although osmotic hydraulic conductivity (Lp r ) decreases upon root exposure to drought 16 , the root hydraulic conductivity of trembling aspen shown an increase under mild stress (exposing roots to a high humidity environment for 17 h) 17 . As previously indicated, Lp r behavior is regulated partially by aquaporin function, specifically by PIPs: In Melaleuca argentea, the partial root-zone drying (PRD) can induce rapid changes in Lp r and aquaporin expression in roots 18 . The Arabidopsis knockout mutants of PIP2;2 shown a lower hydraulic conductivity of root cortex cell compared with the wild type 19 . Overexpression of LeAQP2 gene in root can enhanced hydraulic conductance which induced by arbuscular mycorrhizal fungi 20 . Zhou et al. found
doi:10.1038/srep31814 pmid:27545827 pmcid:PMC4992886 fatcat:y6tn6uyhh5dotlps5jirfqjkxi