Abstract

Plants have complex mechanisms of response to environmental stresses that contribute to stress tolerance. This work is directed at the characterization of four classes of genes that encode proteins involved in the response to environmental stresses: caleosins, the α subunit of heterotrimeric G proteins (GPA1), Pirins and Early-Salt-stress-Induced-3 (Esi3) genes. The work investigates these genes in the model species, Arabidopsis, or the crop specie, wheat. It also characterizes the physical and genetic interaction of members of the caleosins family, GPA1, and Pirin1, to decipher their potential role in signalling pathways related to stress response in plants. The gene families encoding the Pirins and Esi3s were also characterized in hexaploid wheat to investigate possible roles in stress responses.
This work reports that the Arabidopsis caleosins RD20/CLO3 and CLO7 interact both physically and genetically with the Gα subunit, GPA1. The interactions were characterized by Bimolecular Fluorescence Complementation and yeast two-hybrid assays. Interactions were enhanced by both calcium and the GTP bound state of GPA1. RD20/CLO3 and GPA1 play a role in hypocotyl elongation in the dark and in leaf morphology. CLO7 and GPA1 play a role in seed germination in response to ABA treatment and osmotic stress. The clo7 gpa1 double mutant is embryo lethal and cannot be recovered. RD20/CLO3 affects root architecture in response to ABA treatment. Both RD20/CLO3 and CLO7 affect flowering time under long day conditions.
Members of the Triticum aestivum Esi3 and Pirin gene families were implicated in stress response pathways by their differential expression in response to stress treatment. The Esi3 gene family is comprised of 29 family members with 10 paralogs each with a copy in the A, B and D genome except for Esi3-2 which is missing a B copy. All members of the Esi3 gene family have altered gene expression in response to abiotic and biotic stress conditions. The Pirin gene family is comprised of 18 genes with six paralogous gene copies, each having an A, B and D homeolog. The members of the Pirin gene family have specialized expression and play differing roles in response to abiotic and biotic stress.