Stress regulated expression of the GUS-marker gene (uidA) under the control of plant calmodulin and viral 35S promoters in a model fruit tree rootstock: Prunus incisa x serrula.

The fact that calmodulin genes (CaM) are tightly associated with the Ca(2+) regulatory pathway, as well as their putative role in plant defence against pathogens, indicate a potential use of alternative plant promoters to express genes of interest in specific tissues or developmental stages. To study the expression level of the apple CaM promoter, 981 bp sequences upstream were fused to the uidA gene, introduced into cherry and compared with a 35S-GUS construct. Transgene copy number and transgenic expression levels were analysed using Southern blot, Western blot and RT-PCR techniques. Transcription levels were assessed by GUS fluorometry, histochemistry and real-time PCR techniques in leaves of plantlets grown in vitro under various abiotic stresses like low- and high-temperature, salicylic acid and wounding, harvested after 0, 0.5, 1, 2, 4, 10, 24 and 72 h. Histochemical analyses showed staining only in veins and petioles of CaM-GUS lines, while in 35S-GUS plants staining extended to the entire leaf. Furthermore, real-time qPCR data indicate that both promoters are differently regulated by various stresses. Obtained results suggest that the selected apple CaM promoter responsible for the expression of a gene in vascular tissues may offer interesting perspectives for plant defense programs.