The MAMP-Responsive MYB Transcription Factors MYB30, MYB55 and MYB110 Activate the HCAA Synthesis Pathway and Enhance Immunity in Rice

Phenylpropanoids, including diverse compounds, such as monolignols and hydroxycinnamic acids (HCAAs), are essential for land plants to protect them against abiotic stresses, and create physical and chemical barriers to pathogen infection. However, the control of production of these compounds in response to pathogens has been poorly understood. Previously we showed that a MAMP- (microbe-associated molecular pattern) responsive MAPK (mitogen-activated protein kinase) cascade (MKK4-MPK3/MPK6) comprehensively induced the expression of cinnamate/monolignol synthesis genes in rice cells. Here, we identified three MYB proteins, MYB30, MYB55 and MYB110, which are transcriptionally induced by MAMP treatment, MAPK activation and pathogen inoculation. Induced expression of these MYB genes systematically and specifically induced a large part of the genes encoding enzymes in the cinnamate/monolignol pathway. Furthermore, induced expression of the MYB genes caused accumulation of ferulic acid, one of the HCAAs, and enhanced resistance to both fungal and bacterial pathogens in planta. In conclusion, MYB30, MYB55 and MYB110 are involved in the signal pathway between MAMP perception and cinnamate/monolignol synthesis, and have important roles for plant immunity.