Plantview Support Rice Senescence Research: Rice RuBisCO activase promotes the dark-induced leaf senescence by enhancing the degradation of filamentation temperature-sensitive H

New progress has been made in understanding the mechanism of rice leaf senescence under dark conditions.

Professor Yanchun Yu’s team from the School of Life and Environmental Sciences, Hangzhou Normal University, published their findings in the internationally authoritative journal “The Plant Journal” (IF = 6.2, Q1 Top journal).

This study reveals that Rubisco activase (RCA), particularly the RCAL isoform, positively regulates dark-induced senescence (DIS) in rice by promoting the degradation of the temperature-sensitive protein OsFtsH1, providing new insights into the direct regulation of leaf senescence by photosynthesis-related proteins.

Leaf senescence is a critical process in plant development, involving the redistribution of nutrients to support reproductive growth, but its premature onset can lead to a significant decline in crop yields. This process is coordinately regulated by various endogenous factors (such as hormones and age) and exogenous factors (such as darkness, drought, and pathogens). Dark-induced senescence (DIS), as an efficient synchronization model, is widely used to investigate the molecular mechanisms of senescence. Under DIS conditions, leaves exhibit typical characteristics such as chlorophyll degradation, reactive oxygen species (ROS) accumulation, and membrane ion leakage. Meanwhile, senescence-associated genes (SAGs), including members of transcription factor families such as WRKY, NAC, and MYB, are activated and accelerate the senescence process by regulating hormone pathways involving abscisic acid (ABA), jasmonic acid (JA), and other hormones. However, although photosynthesis is known to play a central role in stress responses, how photosynthesis-related proteins directly participate in the regulation of senescence remains unclear.

Rubisco activase (RCA), a key regulatory factor in photosynthesis, promotes carbon fixation by activating the RuBisCO enzyme. Two RCA isoforms (RCAL and RCAS) exist in rice, and they exhibit distinct functions under adverse conditions such as heat stress and drought: RCAL overexpression enhances heat tolerance in rice but increases drought sensitivity, whereas RCAS primarily maintains basal photosynthetic activity. Recent studies have indicated that RCA may extend beyond its traditional photosynthetic functions and participate in various stress responses. For example, it protects thylakoid membranes against oxidative damage under high-temperature conditions and is regulated by the SUB1A transcription factor under submergence stress. However, whether RCA directly participates in the dark-induced senescence pathway has remained unknown.

This study reveals for the first time that RCA, particularly the RCAL isoform, positively regulates DIS progression in rice by modulating the degradation of the zinc metalloprotease OsFtsH1. Dark stress rapidly suppresses RCA transcription and protein expression, while the RCA-deficient mutant (rca) exhibits a significantly delayed senescence phenotype, characterized by a higher chlorophyll retention rate, reduced ROS accumulation, and enhanced photosystem II (PSII) stability. In contrast, RCAL-overexpressing lines exhibit accelerated senescence under dark conditions, and heterologous expression of the same gene in Arabidopsis reproduces this phenotype, indicating that its function is evolutionarily conserved. Mechanistically, RCAL specifically binds to OsFtsH1 in darkness and promotes its degradation through the 26S proteasome pathway. OsFtsH1 itself acts as a negative regulator of senescence: its loss-of-function mutant exhibits accelerated senescence, whereas its overexpression lines show delayed senescence. This discovery establishes the central role of the RCA–OsFtsH1 module in DIS and provides a new perspective on the direct regulation of senescence by photosynthetic proteins.

Experiments using Plantview

The researchers used the PlantView230F Modulated Chlorophyll Fluorescence In Vivo Imaging System from Guangzhou Biolight Biotechnology Co., Ltd. to comparatively observe photosystem II (PSII) function in wild-type plants (NIP), mutants (osftsh1-ami), and overexpression lines (OsFtsH1-OE) under dark stress. The results showed that under normal light conditions, the Fv/Fm images of all three groups of plants displayed a uniform blue-green color (Fv/Fm ≈ 0.8), indicating that their basal PSII function remained intact. However, significant differences emerged following dark treatment: most leaves of the osftsh1-ami mutants retained their blue-green color, indicating the least PSII damage; NIP plants exhibited localized red-yellow areas of damage, indicating a moderate decrease in Fv/Fm; whereas the OsFtsH1-OE overexpression lines displayed extensive red-yellow coloration, indicating a severe reduction in Fv/Fm. These observations directly demonstrate that knockdown of the OsFtsH1 gene enhances PSII stability under dark stress, whereas its overexpression exacerbates photosystem damage, revealing the critical role of the OsFtsH1 protease in regulating the balance between PSII repair and degradation

Doi：10.1111/tpj.17267