The plant hormone auxin regulates many processes central to plant growth and development. There is growing evidence that auxin also plays a role in several interactions between plant-associated microbes and their hosts, including pathogenic microorganisms that cause disease, endophytes, symbionts, and other beneficial microbes that promote plant growth or modulate plant stress responses. Auxin may also influence the development of microbial communities that live in association with plant hosts. It thus comes as no surprise that auxin is also produced or catabolized by diverse microbes to influence host signaling, physiology, and development. Recent studies have revealed that auxin (especially indole-3-acetic acid, IAA) can also act as a signaling molecule that directly impacts microbial gene expression. Thus, auxin appears to function in multiple ways to regulate plant-microbe interactions.

In this Research Topic, we invite authors to submit their work investigating the various ways in which auxin influences host and/or microbial biology, and ultimately the outcome of these interactions. We are especially interested in studies and reports that explore new roles for IAA and other forms of auxin as microbial signals that coordinate the interactions between plant-associated microbes and microbial communities and their plant hosts.

We welcome submissions of all manuscript types, including Original Research, Review and Methods papers that explore, but are not limited to, the following topics:
• Mechanisms of auxin action in regulating host responses to pathogen infection (e.g. promoting host susceptibility or host defense)
• The roles of auxin in promoting beneficial interactions (e.g nodulation, mycorrhizal development)
• The roles of plant or microbial-derived auxin to affect plant development (e.g. size, root architecture)
• Auxin as a microbial signal that modulates gene expression or other aspects of microbial biology in plant-associated microbes
• Auxin as a carbon or nitrogen source for plant-associated microbes
• Biosynthesis and catabolism of auxin in plant-associated microbes (e.g. evolution of biosynthetic pathways and enzymes, regulation of auxin synthesis)
• The role of auxin conjugates in plant-microbe interactions
• Impacts of auxin in the recruitment and/or development of plant-associated microbial communities (e.g. microbiome)
• Dynamic changes of auxin levels, transport, or signaling during plant-microbe interactions

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Frontiers in Plant Science

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