SUMO modification of CaABI5 by CaSIZ1 negatively mediates pepper salt tolerance.

Soil salinization is one of the main issues in the worldwide crop cultivation, which causes inhibition of plant growth, even resulting in a severe reduction in crop yield. Our previous study revealed that CaSIZ1, a putative E3 ligase, is required for pepper SUMOylation and contributes to the salt tolerance. Although an interaction between CaSIZ1 and CaABI5 was detected in the nucleus, it remains elusive how the CaSIZ1-CaABI5 interaction is involved in response to salt stress. In this study, CaABI5 was characterized to play an essential role in pepper salt tolerance. CaABI5 could be significantly induced by ABA and salt stress. Silencing of CaABI5 in pepper led to enhanced salt tolerance, whereas overexpression of CaABI5 in Arabidopsis increased the sensitivity of salt stress. The nucleus-localized CaABI5 was able to be SUMOylated by CaSIZ1 in vitro. CaSIZ1-regulated SUMOylation of CaABI5 not only improved CaABI5 stability under salt stress but also repressed the transcriptional activity of CaABI5. Collectively, these results suggested that the CaSIZ1-CaABI5 module as a negative mediator participates in pepper salt tolerance.