Isolation and analysis of water stress induced genes in maize seedlings by subtractive PCR and cDNA macroarray

In order to identify genes induced during the 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.