Divergent evolutionary pattern of P5CS gene family and drought tolerance verification of LusP5CS1 in linseed

Pyrroline-5-carboxylate synthetase (P5CS), a crucial enzyme encoded by the <italic>P5CS</italic> gene, plays a key role in the drought stress response in plants, primarily by regulating proline biosynthesis. In this study, we used two <italic>P5CS</italic> genes from <italic>Arabidopsis thaliana</italic> as query sequences to meticulously screen and identify members of the P5CS gene family from the genomes of various important grain and oil crops, including linseed, rapeseed, soybean, peanut, sunflower, rice, and wheat. By thoroughly analyzing the selection pressure, specific sites, and functional differentiation potential of <italic>P5CS</italic> genes across these diverse crops, we gained a comprehensive understanding of their evolutionary patterns. Furthermore, we validated the functions of these genes in <italic>Arabidopsis thaliana</italic>, a model organism. Our findings revealed significant differences in gene structure and evolutionary patterns among members of the linseed P5CS gene family compared to their homologs in other crops. Notably, overexpressing the positively selected linseed<italic> LusP5CS1 </italic>gene in <italic>Arabidopsis thaliana</italic> resulted in a substantial increase in proline accumulation and enhanced drought resistance in the transgenic plants. Interestingly, even under non-drought stress conditions, the transgenic <italic>Arabidopsis thaliana</italic> exhibited a notable fitness advantage. This groundbreaking study not only enhances our understanding of the molecular mechanisms underlying drought resistance but also provides a solid theoretical foundation for breeding drought-tolerant linseed varieties.