Location: Plant, Soil and Nutrition ResearchTitle: Clp protease and OR directly control the proteostasis of phytoene synthase, the crucial enzyme for carotenoid biosynthesis in Arabidopsis
|Welsh, R. - University Of Freiburg|
|Zhou, Xiangjun - Cornell University - New York|
|Yuan, Hui - Cornell University - New York|
|Alvarez, Daniel - University Of Freiburg|
|Sun, Tianhu - Cornell University - New York|
|Schlossarek, Dennis - University Of Freiburg|
|Shen, Guoxin - Zhejiang Academy Of Agricultural Sciences|
|Zhang, Hong - Texas Tech University|
|Rodriguez-concepcion, Manuel - Center For Agricultural Research And Training, Cantabria Government (CIFA)|
|Thannhauser, Theodore - Ted|
Submitted to: Molecular Plant
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2017
Publication Date: 1/15/2018
Citation: Welsh, R., Zhou, X., Yuan, H., Alvarez, D., Sun, T., Schlossarek, D., Yang, Y., Shen, G., Zhang, H., Rodriguez-Concepcion, M., Thannhauser, T.W., Li, L. 2018. Clp protease and OR directly control the proteostasis of phytoene synthase, the crucial enzyme for carotenoid biosynthesis in Arabidopsis. Molecular Plant. 11:149-162.
Interpretive Summary: Carotenoids have an important value for human health. Despite significant progress in unravelling regulatory mechanisms of carotenoid biosynthesis, our knowledge on post-translational regulation of carotenoid biosynthetic enzymes remains sparse. In this study, we have identified the plastid Clp protease system as a new player in posttranslational regulation of phytoene synthase (PSY), the critical rate-limiting enzyme of carotenogenesis. We found that PSY interacts with Clp subunits and accumulates as a partially inactive population upon clp deficiency. Moreover, we found that the OR protein is capable to reduce this inactive fraction and counteracts with Clp protease for maintaining PSY amounts and thus activity. In addition, we were also able to add downstream enzymes of the carotenoid biosynthetic pathway to the list of Clp substrates. This study demonstrates that Clp protease and OR maintain the homeostasis of PSY in the plastids to assure optimal enzyme protein abundance for adequate carotenoid biosynthesis in plants.
Technical Abstract: 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 networks, 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, ClpC1, and ClpD). High levels of PSY and several other carotenogenic enzymes over-accumulate in the clpc1, clpp4 and clpr1-2 mutants. The over-accumulated PSY was found to be partially enzymatically active. Loss of the Clp activity in clpc1 results in 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 clpc1, counterbalancing Clp-mediated proteolysis in maintaining PSY protein homeostasis. Collectively, these findings provide novel insights into the quality control of plastid-localized proteins and establish a hitherto unidentified post-translational regulatory mechanism of carotenogenic enzymes in modulating carotenoid biosynthesis in plants.