Cytokinin-mediated repression of jacalin lectins reinforces root immunity

Abstract

The root cap is essential for perceiving environmental cues surrounding the root. However, the molecular mechanisms underlying root cap-mediated immunity and how it defends against invading pathogens remain largely unresolved. Our results indicate that cytokinin plays a major role in regulating soil-borne pathogen such as Ralstonia pseudosolanacearum load around the root and root cap. As Ralstonia populations increase, cytokinin signalling is activated and represses the expression of its downstream signalling targets such as root cap-specific proteins JAL10 and JAL20, to impart the tolerance against the Ralstonia. The functional analysis jacalin-associated lectin family proteins JAL10 and JAL20, revealed that loss-of-function leads to enhance tolerance to Ralstonia whereas gain-of-function leads to susceptibility compared to Col-0. Our Glycoproteomic and metabolomic analyses indicate that JAL10 and JAL20 act as negative regulators of cell wall remodelling and likely to promotes cell wall thickening, thereby enhancing resistance to soil-borne infections. The knockdown of ortholog of JAL protein in Tomato also revealed its conserved function in imparting tolerance to Ralstonia pseudosolanacearum. Further we also show downregulation of JALs by other soil-borne pathogen infection, suggesting that cytokinin might protecting the vulnerable areas of root tip regions by regulating the expression of root cap-specific JALs and thereby fortifying the cell wall.