MicroRNA397 regulates tolerance to drought and fungal infection by regulating lignin deposition in chickpea root

Plants deposit lignin in the secondary cell wall as a common response to drought and pathogen attacks. Cell wall localized multicopper oxidase family enzymes LACCASES (LACs) catalyze the formation of monolignol radicals and facilitate lignin formation. We show an upregulation of the expression of several LAC genes and a downregulation of microRNA397 (CamiR397) in response to natural drought in chickpea roots. CamiR397 was found to target LAC4 and LAC17L out of twenty annotated LACs in chickpea. CamiR397 and its target genes are expressed in root. Overexpression of CamiR397 reduced expression of LAC4 and LAC17L and lignin deposition in chickpea root xylem causing reduction in xylem diameter. Downregulation of CamiR397 activity by expressing a short tandem target mimic (STTM397) construct increased root lignin deposition in chickpea. CamiR397-overexpressing (miR397OX) and STTM397 chickpea lines showed sensitivity and tolerance, respectively, to drought. Infection with a fungal pathogen Macrophomina phaseolina, responsible for dry root rot disease in chickpea, induced local lignin deposition and LAC gene expression. CamiR397-overexpressing and STTM397 chickpea lines showed more sensitivity and tolerance, respectively, to dry root rot. Our results demonstrated the regulatory role of CamiR397 in root lignification during drought and dry root rot in an agriculturally important crop chickpea.