The ABA – GmABI5 – GmCDK8 regulatory axis compromises soybean resistance to Phytophthora sojae

Phytophthora sojae (P. sojae) is a devastating soil-borne oomycete that severely threatens soybean [Glycine max (L.) Merr.] yield and quality. Abscisic acid (ABA) plays critical roles in plant physiology; however, its genetic mechanisms in regulating pathogen resistance remain unclear. Here, we identify ABA as a negative regulator of soybean immunity. The ABA signalling core component Abscisic acid-insensitive 5 (GmABI5) physically interacts with cyclin-dependent kinase 8 (GmCDK8), and they both function as immune suppressors. GmCDK8 stabilizes the GmABI5 protein by partially inhibiting proteasomal degradation, while GmABI5 transcriptionally activates GmCDK8 expression, forming a positive feedback loop that amplifies immune suppression. Furthermore, the GmCDK8-GmABI5 module coregulates overlapping downstream targets to repress pathogen-inducible lignin biosynthesis genes. Our findings highlight the critical roles of GmABI5 and GmCDK8 in P. sojae resistance through interconnection with phytohormone signalling.