CrGEF1, CrGAP1, and CrGDI2 function as key regulators of ROP-GTPase mediated modulation of alkaloid biosynthesis in Catharanthus roseus

ROP-GTPase Regulatory Proteins (RGRPs) have been shown to control plant morphogenesis, development and immunity, however, their role in specialized metabolism is hitherto not known. Here, we demonstrate that specific RGRPs control monoterpene indole alkaloid (MIA) biosynthesis by interacting with distinct Rho of Plants (ROP) in Catharanthus roseus. Among the five Guanine nucleotide Exchange Factors (GEFs), four GTPase-activating proteins (GAPs), and two GDP dissociation inhibitors (GDIs) identified in the C. roseus genome, only CrGEF1, CrGAP1, and CrGDI2 specifically interacted with CrROP3 and CrROP5. These RGRPs displayed distinct cytosolic and/or membrane localization patterns, with their transcripts predominantly expressed in aerial tissues. Functional studies revealed that CrGEF1 acts as a positive regulator of MIA biosynthesis, as its silencing led to a reduction in MIA production, while overexpression enhanced MIA levels. Conversely, CrGAP1 and CrGDI2 function as negative regulators, with their silencing resulting in increased MIA production and their overexpression causing reduced MIA levels. Notably, terminal truncated forms of these RGRPs showed interaction with CrROP3 or CrROP5 but failed to influence MIA biosynthesis, underscoring the importance of these domains in their regulatory functions. Overall, our findings uncover a previously unexplored mechanism by which distinct RGRPs coordinate with specific ROPs to regulate transcription factors and fine-tune MIA biosynthesis in C. roseus. SignificancePlants fine-tune their metabolic pathways to adapt to environmental and physiological cues, balancing primary and specialized metabolism. Here, we uncover a feedback regulatory mechanism by which ROP-GTPase regulatory proteins (RGRPs) control alkaloid biosynthesis in Catharanthus roseus. We found that CrGEF1, CrGAP1, and CrGDI2 specifically interact with ROP-GTPases CrROP3 and CrROP5, modulating the monoterpene indole alkaloid (MIA) pathway. This RGRP-ROP module plays a crucial role in dynamically regulating MIA levels, where CrGEF1 promotes MIA production while CrGAP1 and CrGDI2 act as negative regulators. These findings highlight the importance of RGRP-ROP circuitry in control of alkaloid biosynthesis in C. roseus, and specialized metabolism in plants.