Co-regulation of indole glucosinolates and camalexin biosynthesis by CPK5/CPK6 and MPK3/MPK6 signaling pathways

Secondary plant metabolites, represented by indole glucosinolates (IGS) and camalexin, play important roles inArabidopsisimmunity. Previously, we demonstrated the importance of MPK3 and MPK6, two closely related MAPKs, in regulatingBotrytis cinerea(Bc)-induced IGS and camalexin biosynthesis. Here we report that CPK5 and CPK6, two redundant calcium-dependent protein kinases (CPKs), are also involved in regulating the biosynthesis of these secondary metabolites. The loss-of-function of bothCPK5andCPK6compromises plant resistance toBc. Expression profiling ofCPK5-VKtransgenic plants, in which a truncated constitutively active CPK5 is driven by a steroid-inducible promoter, revealed that biosynthetic genes of both IGS and camalexin pathways are coordinately upregulated after the induction of CPK5-VK, leading to high-level accumulation of camalexin and 4-methoxyindole-3-yl-methylglucosinolate (4MI3G). Induction of camalexin and 4MI3G, as well as the genes in their biosynthesis pathways, is greatly compromised incpk5 cpk6mutant in response toBc. In a conditionalcpk5 cpk6 mpk3 mpk6quadruple mutant,Bcresistance and induction of IGS and camalexin are further reduced in comparison to eithercpk5 cpk6or conditionalmpk3 mpk6double mutant, suggesting that both CPK5/CPK6 and MPK3/MPK6 signaling pathways contribute to promote the biosynthesis of 4MI3G and camalexin in defense againstBc.