Regulation of Chloroplast Protein Import by the Ubiquitin E3 Ligase SP1 Is Important for Stress Tolerance in Plants

摘要

class="head no_bottom_margin" id="sec1title">Results and DiscussionSP1 Expression Levels Influence Abiotic Stress ToleranceBecause SUPPRESSOR OF PPI1 LOCUS1 (SP1) is an important mediator of the chloroplast protein import and proteome changes that occur during plant development [], we wished to investigate whether this E3 ligase is similarly involved in those changes that occur during plant responses to abiotic stress. This possibility was suggested by reports showing that changes in photosynthetic activity and the chloroplast proteome form an important component of plant stress responses []. Thus, we grew sp1 mutant and SP1 overexpressor (OX) Arabidopsis plants under different abiotic stress conditions, starting with high salinity (150 mM NaCl). Mutant plants failed to develop under these conditions, whereas SP1 overexpressors were more stress tolerant than wild-type (A and 1B); in neither case could the developmental and greening differences be accounted for by differences in germination efficiency (C). Similar results were obtained in relation to osmotic stress (300–400 mM mannitol), using both primary leaf emergence and chlorophyll accumulation as measures of stress tolerance (D and A–S1C). By contrast, the different genotypes were indistinguishable when grown on normal medium under the same growth conditions (D).SP1 Expression Levels Influence Abiotic Stress Tolerance(A–C) Plants grown under high-salinity stress were photographed (A) and scored for a measure of stress tolerance (B) and germination efficiency (C). Error bars indicate SEM (n = 3).(D) Plants grown under osmotic stress were scored for a measure of stress tolerance. Error bars indicate SEM (n = 6).(E and F) Plants grown under oxidative stress were photographed (E) and scored for death/survival as a measure of stress sensitivity (F). Error bars indicate SEM (n = 3).