Genome-wide identification and functional characterization of the CaD27 gene family in pepper under cold stress.

Strigolactones (SLs) are crucial phytohormones involved in plant growth and stress adaptation. However, the role of SL biosynthetic genes, particularly CaD27, in pepper under cold stress remains unclear. In this study, we identified three CaD27 genes in the pepper genome, all harboring promoter regions enriched with phytohormone and stress-responsive cis-elements. Functional analysis via virus-induced gene silencing (VIGS) revealed that silencing CaD27.1 or CaD27.3 markedly impaired cold tolerance. Under cold stress, silenced plants exhibited excessive accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA), along with elevated relative electrolyte leakage (REL). Concurrently, antioxidant enzyme activities and the expression of related genes were significantly suppressed. The expression of key cold-responsive genes was also downregulated. Furthermore, abscisic acid (ABA) biosynthesis was compromised, as evidenced by reduced levels of ABA and downregulated expression of ABA synthesis genes (CaNCED1, CaABA2, CaAAO4) and the receptor gene CaPYL2, whereas the ABA catabolism gene CaCYP707A4 remained unchanged. This ABA deficiency led to impaired stomatal closure and exacerbated wilting. Our findings demonstrate that CaD27.1 and CaD27.3 positively regulate cold tolerance in pepper by modulating ROS scavenging and ABA-mediated stomatal responses. Collectively, our findings identify CaD27.1 and CaD27.3 as positive regulators of cold tolerance in pepper and establish them as promising candidate genes for breeding cold-resilient pepper varieties.