Chemical treatment rescues reduced growth of the autoimmune mutant <scp> <i>chs3‐2D</i> </scp> without compromising its immune responses

Plant development in many species including Arabidopsis relies on the accurate balance between growth and defence. A high degree of plant immunity is often accompanied by reduced growth. On the one hand, this growth-defence trade-off depends on the redistribution of metabolic power to either growth or defence. On the other hand, its regulation requires distinct molecular signalling pathways. Reduced growth of the Arabidopsis autoimmune mutant chs3-2D, which shows strong resistance to pathogens, has been rescued by the addition of the low molecular weight compound Ro 8-4304. The application of Ro 8-4304, however, also resulted in a decrease of immune responses to wild-type levels. We applied chemical modification of Ro 8-4304 to identify a derivative that rescues growth of the autoimmune mutant chs3-2D without compromising it immune capacity. In a screening of Ro 8-4304 derivatives, removal of a fluorine atom resulted in the derivative Ro-A03 that rescued growth, but did not affect the increased immune gene expression in chs3-2D. In the presence of Ro-A03 chs3-2D seedlings showed wild-type-like growth, but were more resistant to bacterial pathogens than wild-type seedlings, in line with salicylic acid levels that were higher than in the absence of Ro-A03. We generated a compound by chemical modification that can efficiently rescue growth without decreasing the immune response of the chs3-2D autoimmune mutant.