A type III effector of Xanthomonas arboricola pv. pruni triggers hypersensitive response associated with a MYB-LHC regulatory module in Nicotiana benthamiana

Peach bacterial shot hole, caused by Xanthomonas arboricola pv. pruni ( Xap ), poses a serious threat to global peach production. Although type III effectors (T3Es) of Gram-negative bacteria are known to play crucial roles in plant disease development, their functions in Xap remain poorly characterized. In this study, we employed a Potato virus X (PVX)-based vector to heterologously express 73 Xap T3Es in Nicotiana benthamiana and identified a single effector, Xop-4162, capable of triggering hydrogen peroxide (H₂O₂) accumulation and the hypersensitive response (HR). A central leucine-rich α-helical motif (residues 103-114; SLASLPQLAPLL) was found to be essential for HR induction. Transcriptomic analysis revealed that Xop-4162 significantly downregulated light harvesting complex (LHC) genes and upregulated two R2R3-MYB transcription factor genes, NbMYB-8001 and NbMYB-9001 , in N. benthamiana . Further functional analysis showed that silencing any of three selected LHC genes ( NbLHCa4, NbLHCb1 , and NbLHCb6 ) led to increased H 2 O 2 accumulation. Conversely, transient overexpression of either NbMYB-8001 or NbMYB-9001 strongly suppressed NbLHC transcription and triggered H 2 O 2 accumulation followed by HR, establishing the MYB-LHC as a novel regulatory module in HR induction. Knockout of Xop-4162 strongly reduced bacterial proliferation in peach and significantly compromised pathogenicity, confirming its role as a key virulence factor. Collectively, our findings demonstrate that the Xap T3E Xop-4162 promotes H 2 O 2 accumulation and HR in association with a host MYB-LHC module, providing new insights into the pathogenic mechanisms of peach bacterial shot hole.