Improvement of drought tolerance in maize: towards the functional validation of the Zm-Asr1 gene and increase of water use efficiency by over-expressing C4-PEPC.

Water availability is one of the major limiting factors for plant growth. Maize is particularly sensitive to water stress at reproductive stages with a strong impairment of photosynthesis and grain filling. Here, we describe the use of genetic transformation first to assess the role of a candidate gene Asr1-a putative transcription factor-as an explanation for genetically linked drought tolerance Quantitative Trait Loci (QTLs), and second to modify CO(2) fixation rates in leaves through changes of C(4) phosphoenolpyruvate carboxylase (C(4)-PEPC) activity. Transgenic Asr1 over-expressing lines show an increase in foliar senescence under drought conditions. The highest C(4)-PEPC overexpressing line exhibited an increase (+30%) in intrinsic water use efficiency (WUE) accompanied by a dry weight increase (+20%) under moderate drought conditions. Opposite effects were observed for transgenic plants under-expressing the corresponding proteins. The data presented here indicate the feasibility to increase the level of endogenous biochemical activities related to water economy and/or drought tolerance, and opens a way to develop maize varieties more tolerant to dry growing conditions.