CfCHLM, from Cryptomeria fortunei, Promotes Chlorophyll Synthesis and Improves Tolerance to Abiotic Stresses in Transgenic Arabidopsis thaliana

Abstract

Mg-protoporphyrin IX methyltransferase (CHLM) is essential for the synthesis of chlorophyll (chl). However, no CHLM gene has been reported in Chinese cedar (Cryptomeria fortunei). Here, we cloned the CHLM gene from C. fortunei, and the full-length CfCHLM sequence was 1609 bp, with a 1077 bp ORF region encoding a protein 358 amino acids long. A homologous comparison analysis showed that CfCHLM was highly evolutionarily conserved among different plant species. A phylogenetic tree was drawn using CHLM proteins from ten angiosperms and three gymnosperms, and CfCHLM was found to be most closely related to the TcCHLM protein of Chinese yew (Taxus chinensis). The CfCHLM is located in chloroplasts and does not exhibit self-activation. The expression of CfCHLM was highest in the needles and was downregulated under abiotic stress, i.e., cold, heat, drought, or salt stress. Under cold, heat, drought, and salt abiotic stresses, CfCHLM transgenic A. thaliana showed higher chl fluorescence parameters, elevated chl levels, increased net photosynthetic rate (Pn), and enhanced antioxidant enzyme activities. Conversely, it showed a lower stomatal conductance (Gs), a reduced transpiration rate (Tr), and decreased malondialdehyde (MDA) levels compared to the wild type (WT). In summary, the CfCHLM gene augments chloroplast function, photosynthetic capacity, and stress resistance in plants. This study provides a reference for future research on the growth and development of C. fortunei.