摘要
Phytoene synthase （PSY） is the crucial plastidial enzyme in the carotenoid biosynthetic pathway. However, its post-translational regulation remains elusive. Likewise, Clp protease constitutes a central part of the plastid protease network, but its substrates for degradation are not well known. In this study, we report that PSY is a substrate of the Clp protease. PSY was uncovered to physically interact with various Clp protease subunits （i.e., ClpS1, CIpC1, and CIpD）. High levels of PSY and several other carotenogenic enzyme proteins overac- cumulate in the clpcl, clpp4, and clprl-2 mutants. The overaccumulated PSY was found to be partially enzy- matically active. Impairment of Clp activity in clpcl results in a reduced rate of PSY protein turnover, further supporting the role of Clp protease in degrading PSY protein. On the other hand, the ORANGE （OR） protein, a major post-translational regulator of PSY with holdase chaperone activity, enhances PSY protein stability and increases the enzymatically active proportion of PSY in clpcl, counterbalancing CIp-mediated proteol- ysis in maintaining PSY protein homeostasis. Collectively, these findings provide novel insights into the qual- ity control of plastid-localized proteins and establish a hitherto unidentified post-translational regulatory mechanism of carotenogenic enzymes in modulating carotenoid biosynthesis in plants.
Phytoene synthase （PSY） is the crucial plastidial enzyme in the carotenoid biosynthetic pathway. However, its post-translational regulation remains elusive. Likewise, Clp protease constitutes a central part of the plastid protease network, but its substrates for degradation are not well known. In this study, we report that PSY is a substrate of the Clp protease. PSY was uncovered to physically interact with various Clp protease subunits （i.e., ClpS1, CIpC1, and CIpD）. High levels of PSY and several other carotenogenic enzyme proteins overac- cumulate in the clpcl, clpp4, and clprl-2 mutants. The overaccumulated PSY was found to be partially enzy- matically active. Impairment of Clp activity in clpcl results in a reduced rate of PSY protein turnover, further supporting the role of Clp protease in degrading PSY protein. On the other hand, the ORANGE （OR） protein, a major post-translational regulator of PSY with holdase chaperone activity, enhances PSY protein stability and increases the enzymatically active proportion of PSY in clpcl, counterbalancing CIp-mediated proteol- ysis in maintaining PSY protein homeostasis. Collectively, these findings provide novel insights into the qual- ity control of plastid-localized proteins and establish a hitherto unidentified post-translational regulatory mechanism of carotenogenic enzymes in modulating carotenoid biosynthesis in plants.
