Altered brassinolide sensitivity1 transcriptionally inhibits chlorophyll synthesis and photosynthesis capacity in tomato

Brassinolide (BR) enhances the efficiency of photosynthetic machinery through the activation of metabolic pathways, photochemistry, and ribulose activity. However, the potential transcriptional mechanism mediating these processes through BR signaling still needed to be elucidated. In this study, we found the concealed BR-signaling mediated effects on tomato leaf morpho-physiological and biochemical traits, including chlorophyll accumulation, and photosynthetic efficiency. Under controlled conditions, the altered brassinolide sensitivity1 (abs1) mutant showed decreased leaf area and biomass associated with substantially reduced vascularization and epidermal cell size. abs1 mutant displayed significantly decreased chlorophyll accumulation and suppression in photosynthetic machinery components like photochemical quenching, electron transport rate, the maximal quantum yield of PSII photochemistry, and net photosynthetic rate. Whereas an increase in minimal fluorescence yield and non-photochemical quenching, suggests that abs1 mutant leaf has weakened abilities to harvest and transfer light energy. Moreover, the transcriptome analysis revealed differentially expressed genes involved in the chlorophyll biosynthesis and photosystem (PSI and PSII) reaction center. The abs1 mutant depicted the decreased expression level of genes encoding light-harvesting chlorophyll a/b binding proteins and photosystem II binding protein A required for the reaction center of the PSII complex. In addition, hormonal profiling of the abs1 mutant indicates the complexity of the BR and other phytohormones interactions. Our findings concluded that the BR signaling reduction transcriptionally impairs chlorophyll synthesis, quantum photon harvesting, and light energy transfer, leading to a decrease in photosynthetic capacity.