Seasonal and diurnal variations in gene expression in the desert legume Retama raetam

Studying plants growing naturally within their habitat can contribute greatly to our understanding of molecular and biochemical processes involved in the response of plants to changes in environmental conditions. Seasonal and diurnal variations in the expression of several transcripts involved in the defence of plants against abiotic stresses, i.e. transcripts encoding dehydrins, heat shock proteins, and anti-oxidative enzymes, were followed in Retama raetam plants that grow naturally within an arid dune ecosystem. These were associated with changes in environmental parameters simultaneously recorded at the research sites. It was found that the expression pattern of some transcripts correlated with changes in environmental conditions in the different plants during the year. In contrast, the expression pattern of other transcripts appeared to be plant specific and may be associated with phenotypic variability (plasticity). Transcripts encoding different heat shock proteins were induced in a co-ordinated manner, suggesting that their corresponding products function as a chaperone network. Measurements of photosynthetic activity revealed a diurnal cycle in R. raetam. Photosynthesis was highest during early morning, declined toward the stressful midday hours and recovered at late afternoon. The present analysis suggests that R. raetam uses a combination of different avoidance strategies in co-ordination with active defence mechanisms to withstand the stressful conditions that prevail within the desert ecosystem.