Auxin induces mitogenic activated protein kinase (MAPK) activation in roots of Arabidopsis seedlings

Genome analyses have shown that plants contain gene families encoding vario us components of mitogen activated protein kinase (MAPK) signaling pathways . Previous reports have described the involvement of MAPK pathways in stres s and pathogen responses of leaves and suspension-cultured cells. Here we s how that auxin treatment of Arabidopsis roots transiently induced increases in protein kinase activity with characteristics of mammalian ERK-like MAPK s. The MAPK response we monitored was the result of hormonal action of biol ogically active auxin, rather than a stress response provoked by auxin-like compounds. Auxin-induced MAPK pathway signaling was distinguished genetica lly in the Arabidopsis auxin response mutant axr4, in which MAPK activation by auxin, but not by salt stress, was significantly impaired. Perturbation of MAPK signaling in roots using inhibitors of a mammalian MAPKK blocked a uxin-activated transgene expression in BA3-GUS seedlings, while potentiatin g higher than normal levels of MAPK activation in response to auxin. Data p resented here indicate that MAPK pathway signaling is positively involved i n auxin response, and further suggest that interactions among MAPK signalin g pathways in plants influence plant responses to auxin.