The Papain-like Cysteine Protease from Involved in the Regulation of Growth, Salt Stress Tolerance and Chlorophyll Synthesis in Microalgae.

The papain-like cysteine proteases (PLCPs), the most important group of cysteine proteases, have been reported to participate in the regulation of growth, senescence, and abiotic stresses in plants. However, the functions of PLCPs and their roles in stress response in microalgae was rarely reported. The responses to different abiotic stresses in were often observed, including growth regulation and astaxanthin accumulation. In this study, the cDNA of containing 1515 bp open reading frame (ORF) was firstly cloned from by RT-PCR. The analysis of protein domains and molecular evolution showed that was closely related to from . The expression pattern analysis revealed that it significantly responds to NaCl stress in . Subsequently, transformants expressing in were obtained and subjected to transcriptomic analysis. Results showed that might affect the cell cycle regulation and DNA replication in transgenic , resulting in abnormal growth of transformants. Moreover, the expression of might increase the sensitivity to NaCl stress by regulating ubiquitin and the expression of WD40 proteins in microalgae. Furthermore, the expression of might improve chlorophyll content by up-regulating the expression of NADH-dependent glutamate synthases in . This study indicated for the first time that was involved in the regulation of cell growth, salt stress response, and chlorophyll synthesis in microalgae. Results in this study might enrich the understanding of PLCPs in microalgae and provide a novel perspective for studying the mechanism of environmental stress responses in .