CaSnRK2.4-interacting CaUDP-D (UDP-D-apiose/UDP-D-xylose synthase) positively regulates cold tolerance in Pepper (Capsicum annuum L.).

Pepper (Capsicum annuum L.) is highly sensitive to low-temperature stress, which inhibits plant growth, impairs photosynthesis, disrupts membrane integrity, promotes excessive reactive oxygen species (ROS) accumulation, and ultimately reduces productivity and yield. UDP-D-xylose synthase plays an important role in plant development and abiotic stress responses. However, its underlying mechanism and functional role in response to cold stress in pepper are not well explored. In this study, CaUDP-D was identified as a candidate interacting protein screened from CaSnRK2.4 and subsequently confirmed its interaction through Y2H, Luciferase complementation and BiFC assays. Furthermore, the subcellular localization of CaUDP-D was determined in the nucleus and cell membrane. Functional analysis was performed using VIGS techniques, in which CaUDP-D silenced plants showed severe damage, and significantly reduced cold tolerance, as evidenced by increase cellular damage. For further validation, we conducted the transient overexpression in pepper and stable over expression in Arabidopsis and found that CaUDP-D enhanced cold tolerance. This was indicated by changes in MDA, REL, chlorophyll content and ROS related enzyme activities including SOD, POD, CAT and APX. Together, these results demonstrate that CaUDP-D positively regulates cold tolerance in pepper through ROS homeostasis and cellular protection.