Yu-Qian Niu

Light signals promote photomorphogenesis and photosynthesis, allowing plants to establish photoautotrophic growth. Chloroplasts are organelles responsible for photosynthesis in which light energy is converted into chemical energy and stored as organic matter. However, how light regulates chloroplast photomorphogenesis remains unclear. Here, we isolated a cucumber (Cucumis sativus L.) mutant albino seedling (as) from an ethyl methane sulfonate mutagenesis (EMS) library with an albino phenotype. Map-based cloning revealed that the mutation occurred in a component of cucumber Translocon at Inner membrane of Chloroplasts (CsTIC21). Subsequently, Virus-Induced Gene Silencing (VIGS) and CRISPR/Cas9 analyses confirmed the association between the mutant gene and the as phenotype. Loss-of-function of CsTIC21 induces malformation of chloroplast formation, leading to albinism and death in cucumber. Notably, CsTIC21 transcription was very low in etiolated seedlings grown in the dark and was up-regulated by light, with expression patterns similar to those of Nuclear Factor-YC (NF-YC) genes. Here, seven cucumber NF-YC family genes (CsNF-YC) were identified, among which the expression of four genes (CsNF-YC1, -YC2, -YC9, and -YC13) responded to light. Gene silencing of all CsNF-YC genes in cucumber indicated that CsNF-YC2, -YC9, -YC11-1, and -YC11-2 induced distinct etiolated growth and decreased chlorophyll content. Interaction studies verified that CsNF-YC2 and CsNF-YC9 target the CsTIC21 promoter directly and promote gene transcription. These findings provide mechanistic insights on the role of the NF-YCs–TIC21 module in chloroplast photomorphogenesis promoted by light in cucumber.

Elucidating how the plant species respond to variable light conditions is essential to understand the ecological adaptation to heterogeneous environments. Plant performance and gene regulatory network underpinning the adaptation have been well-documented in sun-grown species. In this study, we surveyed phenotypic and transcriptomic features of four shade-grown and one sun-grown woody species of the family Araliaceae under distinct light conditions. Our phenotypic comparisons demonstrate that the four shade-grown species possess lower light saturation point and higher assimilation ability of the net photosynthetic rate compared to the sun-grown species. In particular, the four shade-grown species maintain similar photosynthesis efficiency in both highlight and lowlight conditions. However, a significantly decreased photosynthesis rate was observed under lowlight condition of the sun-grown species compared to highlight condition. In addition, our leaf anatomical analyses reveal that while all the five species show different anatomical structures under distinct light conditions, the shade-grown species possess lower degree of phenotypic plasticity relative the sun-grown species. Further comparisons of the transcriptome profiling show that all the five species exhibit gene expression divergence among different light conditions. The differentially expressed genes identified in the five species are functionally related to photosynthesis, secondary metabolites and other basic metabolisms. More importantly, differential regulation of the photosynthesis- and photomorphogenesis-related genes are potentially correlated with the phenotypic responses to distinct light conditions of the five species. Our study provides new insights on how the sun- and shade-grown woody species respond to shade and sunlight environments.