Abstract
Lateral root (LR) formation is coordinated by both endogenous and
external factors. As biotic factors, Plant growth-promoting
rhizobacteria (PGPRs) can affect LR formation, while the regulation
mechanism is unclear. In this study, by applying various marker lines,
we found that volatile compounds (VCs) from PGPR strain Bacillus
amyloliquefaciens SQR9 induced a high frequency of oscillation and
prebranch site formation, and further accelerated the development and
emergence of the lateral root primordia (LRP), thus promoting LR
development in model plant Arabidopsis. We demonstrated a
critical role of auxin on SQR9 VCs-induced lateral root formation via
respective mutants and pharmacological experiments. Our results showed
that the YUC9 (YUCs)-mediated auxin biosynthesis, polar auxin transport,
and auxin signaling pathway are involved in SQR9 VCs-induced LRs
formation. We further showed that acetoin, a major component of SQR9
VCs, is less active in promoting root development compared to SQR9
cells, suggesting uncharacterized VCs might contribute to SQR9 effect in
mediating LR formation. In summary, our study revealed a novel mechanism
of PGPR-produced VCs in regulating LR branching in a non-contact manner,
and further efforts will explore useful VCs to promote plant root
development.