Gibberellin indirectly promotes chloroplast biogenesis as ameans to maintain the chloroplast population of expanded cells
Xingshan Jiang1, Heying Li2, Ting Wang2,5, Changlian Peng1, Haiyang Wang3,4, Hong Wu2*, Xiaojing Wang1*
1Guangdong Provincial Key Laboratory of Biotechnology for Plant Development, College of Life Sciences, South China Normal University, Guangzhou 510631, China.
2State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, South China Agricultural University, Guangzhou 510642, China.
3College of Life Sciences, Capital Normal University, Beijing 100048, China.
4Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520-8104, USA.
*Corresponding author: e-mail email@example.com; firstname.lastname@example.org
Chloroplast biogenesis needs to be well coordinated with cell division and cell expansion during plant growth and development to achieve optimal photosynthesis rates. Previous studies showed that gibberellins (GA) regulate many important plant developmental processes, including cell division and cell expansion. However, the relationship between chloroplast biogenesis with cell division and cell expansion and how GA coordinately regulates these processes remain poorly understood. In this study, we showed that chloroplast division was significantly reduced in the GA-deficient mutants of Arabidopsis (ga1-3) and rice (d18-AD), accompanied by reduced expression of several chloroplast division-related genes. However, the chloroplasts of both mutants exhibited increased grana stacking compared to their respective wild-type plants, suggesting that there might be a compensation mechanism linking chloroplast division and grana stacking. A time-lapse analysis showed that cell expansion-related genes tended to be up-regulated earlier and more significantly than the genes related to chloroplast division and cell division in GA-treated ga1-3 leaves, suggesting the possibility that GA may promote chloroplast division through their impact on leaf mesophyll cell expansion. Further, our cellular and molecular analysis of the GA-response signaling mutants suggest that RGA and GAI are the major repressors regulating GA-induced chloroplast division, but other DELLA proteins (RGL1, RGL2 and RGL3) also play a role in repressing chloroplast division in Arabidopsis. Taken together, our data show that GA plays a critical role in controlling and coordinating cell division, cell expansion and chloroplast biogenesis through regulating the DELLA protein family in both dicot and monocot plant species.
Key Words: gibberellin, DELLA proteins, chloroplast biogenesis, chloroplast division, cell expansion, grana stacking.