Physiological, cytological, and transcriptomic analyses reveal temperature response mechanisms in a...

Leaves, as the core organs of photosynthesis, undergo chlorosis that severely compromises photosynthetic performance and reduces crop yield. Temperature is a key environmental factor regulating plant leaf coloration. To decipher the mechanisms underlying temperature-dependent leaf yellowing, this study employed an Ethyl methanesulfonate (EMS)-induced temperature-sensitive leaf yellowing mutant (ly1) of wax gourd and integrated physiological, cytological, and transcriptomic analyses. The results demonstrated that under low-temperature stress, the ly1 mutant exhibited leaf chlorosis, abnormal chloroplast ultrastructure, decreased photosynthetic pigment content, impaired photosynthetic capacity, and significantly reduced biomass. This chlorotic phenotype was reversibly restored upon exposure to elevated temperatures. Transcriptome sequencing and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that differentially expressed genes (DEGs) were significantly enriched in the pathways of photosynthesis and photosynthesis-antenna proteins. Intriguingly, while the temperature-mediated re-greening occurred without a coordinated upregulation of chlorophyll biosynthesis genes, implying post-transcriptional control, the expression of genes encoding core complexes of photosystem I (PSI) and photosystem II (PSII), as well as light-harvesting complex (LHC) proteins, was significantly lower in ly1 leaves under low temperature compared to the wild type (WT, DZ163). Under high-temperature (35°C) recovery conditions, two Lhcb1-encoding genes, BhiUN644G2 and Bhi11G001128, were specifically upregulated in the mutant. Their expression patterns were further validated by quantitative real-time polymerase chain reaction (qRT-PCR), suggesting their potential role as key regulatory factors driving leaf re-greening. This study not only provides valuable genetic material for in-depth analysis of the regulatory network governing the temperature response of the photosynthetic apparatus in plants, but the identified key genes also offer potential targets for improving temperature adaptability in crops.