Genome-wide analysis of ascorbate peroxidase and functional characterization of SpAPX249b and SpAPX285c for salt tolerance in Sesuvium portulacastrum

Ascorbate peroxidase (APX) is a vital antioxidant enzyme, involving in plant development and stress response by scavenging excessive reactive oxygen species (ROS). The APX genes have been characterized in many organisms, however, its role in Sesuvium portulacastrum has not yet to be fully investigated. Here, we identified 33 SpAPXs from the the genome of S. portulacastrum, and found them to be divided into five subgroups across the 16 chromosomes. Cis-element analysis of their promoters indicated that all the detected SpAPXs show potential roles in response to biotic and abiotic stresses as well as phytohormone effects on the plant growth and development. Transcriptomic data of the different tissues revealed that the 9 SpAPX genes were specifically expressed in root and 13 SpAPX genes were specifically expressed in leaves, with SpAPX249b prominently expressed in root and SpAPX285c prominently expressed in leaves. Moreover, quantitative real-time PCR analysis revealed that both SpAPX249b and SpAPX285c genes expressed only after NaCl application and were sharply induced in the high concentration of NaCl treatments. Our findings suggest that SpAPX249b and SpAPX285c may be associated with palnt salt tolerance and can serve as valuable genes for enhancing salt tolerance in other plants.