Structural and functional characterisation of two novel durum wheat annexin genes in response to abiotic stress.

Abiotic stress results in massive loss of crop productivity throughout the world. Understanding the plant gene regulatory mechanisms involved in stress responses is very important. Annexins are a conserved multigene family of Ca-dependent, phospholipid-binding proteins with suggested functions in response to environmental stresses and signalling during plant growth and development. Annexins function to counteract oxidative stress, maintain cell redox homeostasis and enhance drought tolerance. A full-length cDNA of two genes (TdAnn6 and TdAnn12) encoding annexin proteins were isolated and characterised from Tunisian durum wheat varieties (Triticum turgidum L. subsp. durum cv. Mahmoudi). Analyses of the deduced proteins encoded by annexin cDNAs (TdAnn6 and TdAnn12) indicate the presence of the characteristic four repeats of 70-75 amino acids and the motifs proposed to be involved in Ca2+ binding. Gene expression patterns obtained by real-time PCR revealed differential temporal and spatial regulation of the two annexin genes in durum wheat under different abiotic stress conditions such as salt (NaCl 150mM), osmotic (10% polyethylene glycol 8000), ionic (LiCl 10mM), oxidative (H2O2), ABA (100µM), salicylic acid (10mM), cold (4°C) and heat (37°C) stress. The two annexin genes were not regulated by heavy metal stress (CdCl2 150µM). Moreover, heterologous expression of TdAnn6 and TdAnn12 in yeast improves its tolerance to abiotic stresses, suggesting annexin's involvement in theses stress tolerance mechanisms. Taken together, our results show that the two newly isolated wheat annexin might play an active role in modulating plant cell responses to abiotic stress responses.