The endophytic fungus Serendipita indica alters auxin distribution in
Arabidopsis thaliana roots through alteration of auxin transport and
conjugation to promote plant growth
Abstract
Plants 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 of Arabidopsis thaliana with the beneficial root
colonizing endophyte Serendipita indica represents a well-studied
system. Co-colonization of Arabidopsis roots with S. indica
significantly 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 which S. indica promotes 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 between A. thaliana and S. indica. Our
experiments revealed the essential role of tightly controlled auxin
conjugation in the plant–fungus interaction. It particularly
highlighted the importance of two GRETCHEN HAGEN 3 ( GH3)
genes, GH3.5 and GH3.17, 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 the PIN2
auxin transporter gene in roots of Arabidopsis seedlings infected with
S. indica and demonstrate that this transcriptional adjustment
affects auxin signaling in roots, which results in increased plant
growth.