Distinct immune pathways activated by harpin proteins in Sorghum bicolor.

This study investigates how two harpin proteins, HrpZ and Hpa1, modulate plant immunity as potential alternatives to pesticides. Despite the established importance of SA in immunity, its regulatory complexity and gene expression dynamics are partially elucidated. We examined the effect of HrpZ and Hpa1 on the SA signalling pathway and the expression of seven marker genes (NPR1, EDS1, CAD1, NSL1, AED3, AED4, WRKY8) identified through existing microarray dataset analysis and analysed by qRT-PCR and HPLC. Our findings reveal distinct modes of action: HrpZ strongly activates SA-mediated immunity by upregulating SA levels and SA-responsive genes. Conversely, Hpa1 does not significantly impact SA levels but upregulates AED3 and AED4, suggesting an alternative, SA-independent defence mechanism. This research provides valuable insights into harpin-induced plant immunity, paving the way for targeted biostimulant development in sustainable agriculture. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-025-01601-6.