Elucidation of a photoacclimation role for chloroplast-localized serine peptidase, cAAP, in Arabidopsis thaliana

Peptidases are involved in many aspects of plant physiology, including protein turnover in response to stress and initiation of cell death/senescence. Peptidases are localized to various organelles within the plant cell. At5g36210 encodes cAAP, a chloroplast-localized acyl aminoacyl peptidase that may function in protein turnover in response to high light intensity or chlorophyll availability, as was proposed for its ortholog, cGEP. A role for cAAP in photoacclimation was examined by measuring chlorophyll and anthocyanin accumulation in seedlings possessing overexpression constructs of cAAP and in a line that has a large insertion that inactivates the cAAP gene creating a caap null mutation. Accumulation of chlorophyll and anthocyanin were then measured under light stress and non-stress conditions. Similar to cGEP, the results suggested cAAP did not have a role in photoacclimation. Accumulation of chlorophyll after growth in darkness was also measured for cAAP overexpression and caap null lines; however, differences in greening attributable to cAAP could not be detected due to the variability observed in the rate of greening for different seed stocks.