The endophytic fungusSerendipita indicaalters auxin distribution inArabidopsis thalianaroots through alteration of auxin transport and conjugation to promote plant growth

Abstract

AbstractPlants share their habitats with a multitude of different microbes. This close vicinity promoted the evolution of inter-organismic interactions between plants and many different microorganisms that provide mutual growth benefits both to the plant and the microbial partner. The symbiosis ofArabidopsis thalianawith the beneficial root colonizing endophyteSerendipita indicarepresents a well-studied system. Co-colonization of Arabidopsis roots withS. indicasignificantly promotes plant growth. Due to the notable phenotypic alterations of fungus-infected root systems, the involvement of a reprogramming of plant hormone levels, especially that of indole-3-acetic acid, has been suggested earlier. However, until now, the molecular mechanism by whichS. indicapromotes plant growth remains largely unknown. This study used comprehensive transcriptomics, metabolomics, reverse genetics, and life cell imaging to reveal the intricacies of auxin-related processes that affect root growth in the symbiosis betweenA. thalianaandS. indica. Our experiments revealed the essential role of tightly controlled auxin conjugation in the plant–fungus interaction. It particularly highlighted the importance of twoGRETCHEN HAGEN 3(GH3) genes,GH3.5andGH3.17, for the fungus infection-triggered stimulation of biomass production, thus broadening our knowledge about the function of GH3s in plants. Furthermore, we provide evidence for the transcriptional alteration of thePIN2auxin transporter gene in roots of Arabidopsis seedlings infected withS. indicaand demonstrate that this transcriptional adjustment affects auxin signaling in roots, which results in increased plant growth.