Harnessing light-harvesting chlorophyll a/b-binding proteins for multiple abiotic stress tolerance in Chlamydomonas reinhardtii: Insights from genomic and physiological analysis.

Light-harvesting chlorophyll a/b-binding proteins (LHC) of photosystem II perform key functions in various processes, e.g., photosynthesis, development, and abiotic stress responses. Nonetheless, comprehensive genome-wide investigation of LHC family genes (CrLHCs) has not been well-reported in single-cell alga (Chlamydomonas reinhardtii). Here, we discovered 61 putative CrLHC genes in the C. reinhardtii genome and observed that most genes demonstrate stable exon-intron and motif configurations. We predicted five phytohormones- and six abiotic stress-interrelated cis-regulatory elements in promoter regions of CrLHC. Likewise, 19 miRNAs targeting 42 CrLHC genes from 16 unique families were discovered. Besides, we identified 400 transcription factors from 13 families, including ERF, GATA, CPP, bZIP, C3H, MYB, SBP, Dof, bHLH, C2H2, G2-like, etc. Protein-protein interactions and 3D structures provided insight into CrLHC proteins. Gene ontology and KEGG-based enrichment advocated their role in light responses, photosynthesis, and energy metabolisms. Expression analysis highlighted the shared and unique roles of many CrLHC genes against different abiotic stresses (UV-C, green light, heat, nitric oxide, cadmium, nitrogen starvation, and salinity). Under salinity stress, antioxidant enzyme activity, reactive oxygen species markers, photosynthesis-related traits and pigments were significantly affected. Briefly, this comprehensive genomic and physiological study shed light on the impact of CrLHC genes in abiotic stress tolerance and set the path for future genetic engineering experiments.