Rhizobacterial volatiles and photosynthesis‐related signals coordinate MYB 72 expression in Arabidopsis roots during onset of induced systemic resistance and iron‐deficiency responses

Abstract

Summary: In Arabidopsis roots, the transcription factor MYB 72 plays a dual role in the onset of rhizobacteria‐induced systemic resistance (ISR) and plant survival under conditions of limited iron availability. Previously, it was shown that MYB 72 coordinates the expression of a gene module that promotes synthesis and excretion of iron‐mobilizing phenolic compounds in the rhizosphere, a process that is involved in both iron acquisition and ISR signaling. Here, we show that volatile organic compounds (VOC s) from ISR‐inducing Pseudomonas bacteria are important elicitors of MYB 72. In response to VOC treatment, MYB 72 is co‐expressed with the iron uptake‐related genes FERRIC REDUCTION OXIDASE 2 (FRO 2) and IRON‐REGULATED TRANSPORTER 1 (IRT 1) in a manner that is dependent on FER‐LIKE IRON DEFICIENCY TRANSCRIPTION FACTOR (FIT), indicating that MYB 72 is an intrinsic part of the plant's iron‐acquisition response that is typically activated upon iron starvation. However, VOC‐induced MYB 72 expression is activated independently of iron availability in the root vicinity. Moreover, rhizobacterial VOC‐mediated induction of MYB 72 requires photosynthesis‐related signals, while iron deficiency in the rhizosphere activates MYB 72 in the absence of shoot‐derived signals. Together, these results show that the ISR‐ and iron acquisition‐related transcription factor MYB 72 in Arabidopsis roots is activated by rhizobacterial volatiles and photosynthesis‐related signals, and enhances the iron‐acquisition capacity of roots independently of the iron availability in the rhizosphere. This work highlights the role of MYB 72 in plant processes by which root microbiota simultaneously stimulate systemic immunity and activate the iron‐uptake machinery in their host plants.