Oral Presentation International Plant Molecular Biology Conference 2024

BPG4 maintained chloroplast homeostasis by suppressing GLK transcription factors downstream of light and brassinosteroid signaling (#289)

Ryo Tachibana 1 , Susumu Abe 2 3 , Momo Marugami 2 3 , Ayumi Yamagami 1 , Rino Akema 1 , Takao Ohashi 1 , Kaisei Nishida 1 , Shohei Nosaki 4 , Takuya Miyakwa 1 , Masaru Tanokura 5 , Jong-Myong Kim 2 5 6 , Motoaki Seki 2 , Takehito Inaba 7 , Minami Matsui 2 , Kentaro Ifuku 8 , Tetsuo Kushiro 3 , Tadao Asami 5 , Takeshi Nakano 1 2
  1. Kyoto University, Kyoto, KYOTO, Japan
  2. CSRS, RIKEN, Yokohama, Kanagawa, Japan
  3. School of Agriculture, Meiji University, Kawasaki, Kanagawa, Japan
  4. Faculty of Life and Environmental Sciences, Tsukuba University, Japan
  5. Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo, Japan
  6. Ac-Planta Inc., Tokyo, Japan
  7. Faculty of Agriculture, University of Miyazaki, Miyazaki, Japan
  8. Graduate School of Agriculture, Kyoto University, Kyoto, Japan

Chloroplast development adapts to the environment for performing suitable photosynthesis. Brassinosteroids (BRs), plant steroid hormones, have crucial effects on not only plant growth but also chloroplast development. However, the detailed molecular mechanisms of BR signaling in chloroplast development remain unclear. Here, we identified a novel regulator of chloroplast development, BPG4, involved in light and BR signaling1. BPG4 encodes a functionally unknown protein that is evolutionally conserved across land plants. BPG4 deficiency increased chlorophyll contents and promoted chloroplast development. BPG4 suppressed the expression of photosynthesis-associated nuclear genes (PhANGs) in the nucleus. BPG4 interacted with GOLDEN2-LIKE (GLK) transcription factors that promote the expression of PhANGs and chloroplast development, and suppresses their activities. BPG4 expression was activated by BR deficiency and suppressed by the BR signaling master transcription factor BES1. BPG4 was expressed specifically in photosynthetic tissues in the light and was regulated by the circadian rhythm. Given that both BR deficiency and light promote chloroplast development, the dynamics of BPG4 expression appeared to be opposite and inconsistent with those of BPG4 protein function to suppress chloroplast development. Nevertheless, the viewpoint of maintaining homeostasis for chloroplasts would be able to resolve this contradiction and hypothesize the actual role and physiological significance of BPG4 in plant growth. Finally, we revealed that BPG4 deficiency causes increased reactive oxygen species (ROS) generation and damage to photosynthetic activity under excessive high-light conditions. Our findings suggest that BPG4 acts as a chloroplast homeostasis factor by fine-tuning the expression of PhANGs, optimizing chloroplast development, and avoiding ROS generation.

  1. Tachibana, R., Abe, S., Marugami, M. et al. BPG4 regulates chloroplast development and homeostasis by suppressing GLK transcription factors and involving light and brassinosteroid signaling. Nat Commun 15, 370 (2024). https://doi.org/10.1038/s41467-023-44492-5