Summary Chlorophagy removes photodamaged chloroplasts in plants, while individual chloroplasts are also protected by mechanisms that limit damage to the photosynthetic apparatus caused by excess light energy, known as photoinhibition. How chlorophagy is functionally coupled with chloroplast‐level protective mechanisms during acclimation to photoinhibition remains unclear. We investigated acclimatory responses to photoinhibition at the intracellular level in Arabidopsis thaliana through an integrative analysis combining Chl fluorescence measurements, microscopy imaging, and genetic analyses using mutants defective in nonphotochemical quenching (NPQ) or the chloroplast avoidance response. The functionality of individual chloroplasts was further assessed by Chl fluorescence lifetime imaging and probe‐based visualization of singlet oxygen and starch. Severe photoinhibition of photosystem II precedes the appearance of abnormally swollen chloroplasts, which are subsequently recognized by the autophagy machinery for degradation. The swollen chloroplasts represent irreversibly damaged chloroplasts that accumulate reactive oxygen species and lose photosynthetic function. The formation of these nonfunctional chloroplasts was enhanced in mutants defective in NPQ or the chloroplast avoidance response, and hyperaccumulation of nonfunctional chloroplasts led to necrotic cell death. Together, our findings illustrate how multilayered responses coordinate acclimation to photoinhibition: Chloroplast protective mechanisms minimize the formation of nonfunctional chloroplasts while chlorophagy removes them when they arise.
Summary Plant regeneration underpins crop genetic improvement, yet its regulatory mechanism remains poorly characterized in woody fruit trees. The RWP‐RK domain‐containing (RKD) transcription factor CitRWP acts as a pleiotropic regulator of nucellar polyembryony and somatic embryogenesis (SE) in citrus, but its downstream molecular network remains elusive. We demonstrate that CsWUS, a core stem cell regulator, is a direct downstream target of CitRWP. CitRWP binds to the CsWUS promoter to activate its transcription. Additionally, CitRWP interacts with the SWItch/Sucrose Non‐Fermentable (SWI/SNF) chromatin‐remodeling ATPase SPLAYED (SYD), synergistically enhancing CsWUS activation, while chromatin accessibility at the CsWUS locus is enhanced upon CitRWP overexpression. We further uncover that CsWUS negatively regulates CitRWP expression via a feedback loop. CsWUS overexpression promotes SE in recalcitrant citrus callus, but causes abnormal meristem proliferation and impairs shoot organogenesis from epicotyl segments. CsWUS greatly enhanced in planta transformation efficiency in the model citrus. This study establishes the CitRWP – CsWUS regulatory axis as a central module that coordinates multiple developmental fate transitions in association with chromatin remodeling, providing novel insights into the mechanisms of cellular totipotency and plant regeneration.
Summary Seed traits underpin plant regeneration and are central to predicting species' responses to environmental change, yet their intraspecific variability remains poorly integrated into trait‐based frameworks. Progress has been limited by the conflation of processes operating across nested levels, from regions and populations to mother plants and individual seeds, and by weak integration of genetic drivers with environmental and phenotypic data. Drawing on published literature and analyses of seed traits in wild tree populations, we show that substantial seed‐trait variation can occur among mother plants and individual seeds within populations, meaning that population‐level macroenvironmental variables often capture only part of the observed variation. To address these limitations, we propose a roadmap to disentangle hierarchical drivers of intraspecific trait variability (ITV) in seeds. We outline a strategic plan to quantify seed‐trait variation across hierarchical levels, investigate its drivers where variation is concentrated, and assess its consequences for recruitment and demographic outcomes. We recommend coordinated, standardised sampling and experiments that retain mother‐plant and individual‐seed identity, integrate genetic, environmental and phenotypic data, and use scalable approaches to link seed traits to performance across recruitment stages. Recognising and integrating ITV across nested levels is essential for improving predictions of plant regeneration under environmental change.
