Interference with Clp protease impairs carotenoid accumulation during tomato fruit ripening

Authors: D'ANDREA, LUCIO - National Center For Agriculture And Forestry Technologies (CENTA); SIMON-MOYA, MIQUEL - National Center For Agriculture And Forestry Technologies (CENTA); LIORENTE, BRIARDO - National Center For Agriculture And Forestry Technologies (CENTA); LLAMAS, ERNESTO - National Center For Agriculture And Forestry Technologies (CENTA); MARRO, MONICA - National Center For Agriculture And Forestry Technologies (CENTA); LOZA-ALVAREZ, PABLO - National Center For Agriculture And Forestry Technologies (CENTA); Li, Li; RODRIGUEZ-CONCEPCION, MANUEL - National Center For Agriculture And Forestry Technologies (CENTA)

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2017
Publication Date: 1/29/2018
Citation: D'Andrea, L., Simon-Moya, M., Liorente, B., Llamas, E., Marro, M., Loza-Alvarez, P., Li, L., Rodriguez-Concepcion, M. 2018. Interference with Clp protease impairs carotenoid accumulation during tomato fruit ripening. Journal of Experimental Botany. 69:1557-1568.

Interpretive Summary: Tomato fruit ripening is characterized by color change and carotenoid accumulation in chromoplasts. The Clp protease system is known to play a key role in maintaining protein homeostasis in plastids. This study investigates whether the Clp protease complex also has a role in regulation of carotenoid accumulation during tomato ripening. By silencing one of the Clp protease subunit to reduce Clp protease activity in ripening fruit, this work shows that the Clp protease plays a role for carotenoid biosynthesis and accumulation, most probably in co-ordination with tomato ClpB3 and OR chaperones to alleviate protein folding stress, promote enzyme stability and accumulation, and prevent carotenoid degradation.

Technical Abstract: Profound metabolic and structural changes are required for fleshy green fruits to ripen and become colorful and tasty. In tomato (Solanum lycopersicum), fruit ripening involves the differentiation of chromoplasts, specialized plastids that accumulate carotenoid pigments such as Beta-carotene (pro-vitamin A) and lycopene. Here, we explored the role of the plastidial Clp protease in chromoplast development and carotenoid accumulation. Ripening-specific silencing of one of the subunits of the Clp proteolytic complex resulted in Beta-carotene-enriched fruits that appeared orange instead of red when ripe. Clp-defective fruit displayed aberrant chromoplasts and up-regulated expression of nuclear genes encoding the tomato homologs of Orange (OR) and ClpB3 chaperones, most probably to deal with misfolded and aggregated proteins that could not be degraded by the Clp protease. ClpB3 and OR chaperones protect the carotenoid biosynthetic enzymes deoxyxylulose 5-phosphate synthase and phytoene synthase, respectively, from degradation, whereas OR chaperones additionally promote chromoplast differentiation by preventing the degradation of carotenoids such as Beta-carotene. We conclude that the Clp protease contributes to the differentiation of chloroplasts into chromoplasts during tomato fruit ripening, acting in co-ordination with specific chaperones that alleviate protein folding stress, promote enzyme stability and accumulation, and prevent carotenoid degradation.