CSB Special Seminar: Novel brassinosteroid signaling factors BIL7 and BPG4 regulate plant development and chloroplast biogenesis – TAKESHI NAKANO, PhD – Grad. Sch. Biostudies, Kyoto Univ., Kyoto, JAPAN

CSB Special Seminar: 

TAKESHI NAKANO, PhD

Grad. Sch. Biostudies, Kyoto Univ., Kyoto, JAPAN

TITLE: Novel brassinosteroid signaling factors BIL7 and BPG4 regulate plant development and chloroplast biogenesis

ABSTRACT:

Plant growth begins with photosynthesis to fix carbon into the plant biomass, and subsequently continues to cell differentiation, division, and elongation, which utilize the assimilated carbon.  As brassinosteroids (BRs) are known for their dual role in regulating plant development and chloroplast biogenesis, analyzing both regulatory mechanisms from the perspective of BR signaling would provide valuable insights into the mechanisms of plant growth.

BIL1/BZR1, a master transcription factor that regulates approximately 3,000 genes by its non-canonical structure as a bHLH transcription factor in the BR signaling pathway (1,2). Though BIL1/BZR1 is transported to the nucleus from the cytosol in response to BR signaling, the molecular mechanism underlying this process is unknown. Here, we identify a novel BR signaling factor, Brz-INSENSITIVE-LONG HYPOCOTYL7 (BIL7), that enhances the resistance to the BR biosynthesis inhibitor Brz and plant height to increase cell division. BIL7 is mainly localized to the plasma membrane, but during the early stages of cell growth, it was also localized to the nucleus. BIL7 was found to bind to BIL1/BZR1, and nuclear accumulation of BIL1/BZR1 was strongly enhanced by BIL7 overexpression. Our findings suggest that BIL7 mediates nuclear accumulation of BIL1/BZR1, which activates inflorescence elongation in plants via BR signaling (3).

BRs have crucial effects on not only plant growth but also chloroplast development. Here, we identify a novel regulator of chloroplast development, Brz-INSENSITIVE-PALE GREEN4 (BPG4), involved in light and BR signaling. BPG4 interacts with GLK transcription factors that promote the expression of photosynthesis-associated nuclear genes (PhANGs), and suppresses their activities, thereby causing a decrease in the amounts of chlorophylls and the size of light-harvesting complexes. BPG4 expression is induced by BR deficiency and 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 optimizing chloroplast development and avoiding ROS generation (4).

HOST: Yoshioka Lab

LOCATION: ES3087