Isolation And Analysis Of Water Stress Induced Genes In Maize (Zea Mays. L) Seedlings

Water stress is one of the major environmental stresses that adversely affect plant growth and crop yield worldwide. Hundreds of genes are thought to be involved in abiotic stress responses. However, only a few molecular components have been known precisely until recently. Most of these studies were processed in model plant Arabidopsis.To identify the genes controlling water stress response in maize (Zea mays) seedlings, suppression subtractive hybridization (SSH) was performed using mixed cDNAs prepared from maize seedlings treated with 20% PEG as testers and cDNAs from unstressed maize seedlings as drivers. A forward subtractive cDNA library was constructed, from which 960 recombinant colonies were picked and amplified. Through differential screening of the subtractive cDNA library, 533 clones were identified as water stress induced. After sequencing, 190 unique expressed sequence tags (ESTs) were obtained by clustering and blast analysis, which included transcripts that had previously been reported as responsive to stress as well as some functionally unknown transcripts. The ESTs with significant protein homology were sorted into 13 functional categories.A cDNA marcoarray containing the 190 unique ESTs was used to analyze their expression profiles in maize seedling during both PEG treatment and natural drought. The results indicated that 67 ESTs in leaves and 113 ESTs in roots were significantly up-regulated by PEG-stress. 123 ESTs were found to be up-regulated for at least one time-course point in either maize leaves or roots. Correspondingly, 163 ESTs were significantly up-regulated by drought stress. Results from the hierarchical cluster analysis suggest that the leaves and roots of maize seedlings had different expression profiles after PEG treatment and that there was a lot of overlap between PEG- and drought-stress induced up-regulated transcripts. A set of transcripts has been identified, which have significantly increased expression and probably involved in water stress signaling pathway based on data analysis.Among the 190 unique cDNA clones, one clone which shows 100% identity to maize GST7 gene and is identified as ZmGST7. Northern analysis indicated that ZmGST7 is induced by water stress and had highly expression level in the late time point. In order to investigate the function of ZmGST7, two vectors were constructed and introduced to Arabidopsis thaliana by Agrobacterium tumefaciens. Some transgenic T2 lines were used for molecular and tolerance analysis. The preliminary results indicated that transgenic Arabidopsis seedlings that overexpress ZmGST7 grow faster than wild type seedlings and may plays certain roles in lower osmotic stress.In the present study, we also identified many PEG-, drought-, ABA-, salt-, cold-inducible cDNAs. However, the functions of most of them remain unknown. It is important to analyze the functions oftheir corresponding full-length genes not only for further understanding the molecular mechanisms of stress response in higher plants but also for improving the stress tolerance of crops by genetic manipulation.