The Deg5 and Deg8 thylakoid lumenal proteases are dispensable for photosynthesis and fruit ripening in Solanum lycopersicum

Abstract

‘Deg’ is a family of soluble ATP-independent serine proteases, with plant Deg1, Deg5 and Deg8 localized to the chloroplast thylakoid lumen. These three proteases have been mostly studied with regard to the repair of damaged photosystem II (PSII) complexes during photoinhibition. The requirement of Deg5 and Deg8, proposed to work together as a heterohexamer, to PSII repair in Arabidopsis is debated. This, together with our interest in exploring the involvement of chloroplast proteases in the chloroplast-to-chromoplast transition, during which the thylakoid network is dismantled, prompted us to study the lumenal Deg proteases in tomato (Solanum lycoperiscum) plants. Toward this, we generated tomato knockout plants and focused on leaf photosynthesis and on fruit development and ripening. Lack of SlDeg1 resulted in chlorotic leaves and considerably impaired plant growth. On the other hand, mutants lacking both SlDeg5 and SlDeg8 were very similar to WT plants, and had neither impaired nor enhanced photosynthetic performance at different controlled or variable conditions. Monitoring fruit development and ripening, as well as fruit characteristics and plant yield showed that they were not affected in sldeg5/8 mutants. We thus propose that SlDeg5 and SlDeg8 are not essential for photosynthesis and fruit ripening in tomato plants.