Arabidopsis HFR1 Is a Potential Nuclear Substrate Regulated by the Xanthomonas Type III Effector XopD(Xcc8004)

XopD(Xcc8004), a type III effector of Xanthomonas campestris pv. campestris (Xcc) 8004, is considered a shorter version of the XopD, which lacks the N-terminal domain. To understand the functions of XopD(Xcc8004), in planta, a transgenic approach combined with inducible promoter to analyze the effects of XopD(Xcc8004) in Arabidopsis was done. Here, the expression of XopD(Xcc8004), in Arabidopsis elicited the accumulation of host defense-response genes. These molecular changes were dependent on salicylic acid and correlated with lesion-mimic phenotypes observed in XVE::XopD(Xcc8004) transgenic plants. Moreover, XopD(Xcc8004) was able to desumoylate HFR1, a basic helix-loop-helix transcription factor involved in photomorphogenesis, through SUMO protease activity. Interestingly, the hfr1-201 mutant increased the expression of host defense-response genes and displayed a resistance phenotype to Xcc8004. These data suggest that HFR1 is involved in plant innate immunity and is potentially regulated by XopD(Xcc8004).