Abstract:

Cysteine proteinases（CPs）play significant roles in salt stress responses of plants, thus the function of CaCP1 in salt resistance was studied by cloning CaCP1, which may provide reference for the breeding of pepper salt resistant varieties. First, the CaCP1 promoter of pepper（Capsicum annuum L.）was cloned, then recombinant vector with different length promoter fragments was constructed based on cis-regulatory elements associated with salt stress, and transient transformation of tobacco was performed. Salt treatment was carried out on T₃ generation tobacco transgenic lines overexpressing CaCP1, phenotype symptoms were observed, physiological indexes were measured, and the expressions of stress-related genes were analyzed. The results revealed that in response to salt treatment, the GUS expression in -410 to -1 bp region was the strongest. The leaves of CaCP1 transgenic plants wilted and yellowed earlier. The chlorophyll and relative water content were significantly lower than those of wild type, while MDA and electrolyte leakage rates were significantly higher than those of wild-type. ROS scavenger enzymes CAT and SOD activities decreased, while POD activity increased. Compared to wild-type, the expressions of ROS-scavenging genes（NtSOD, NtPOD, NtCAT, and NtAPX）and salt stress-related genes（NtLEA5, NtNHX1, NtP5CS1, and NtSOS1）significantly decreased. CaCP1 acts as a negative regulator to mediate the plant defense response to salt stress.

Key words: pepper, cysteine proteinase, transgenic, tobacco, salt stress