Rhizosphere bacteria mediate flowering time of two genotypes of Arabidopsis with and without root-secreted signaling (-)-loliolide

Despite increasing knowledge of plant flowering involved in rhizosphere and soil microbes, little is known about root-secreted signaling molecules recruiting microbes in general, or on the rhizosphere bacteria and flowering time in particular. Here, we experimentally showed the flowering time of Arabidopsis thaliana (Arabidopsis) shift with root signaling molecules and rhizosphere bacteria. Compared to wild-type Arabidopsis (WT) with a ubiquitous signaling (-)-loliolide, flowering time of carotenoid-deficient Arabidopsis mutant (szl1-1) without rootsecreted (-)-loliolide was significant early, resulting in differential rhizosphere and soil bacterial communities between WT and szl1-1. More significant differences occurred in rhizosphere soil rather than in bulk soil. There were differences in rhizosphere bacteria and community functions between two genotypes of Arabidopsis. The biomarker genera Rhizobacter, Burkholderia, Mucilaginibacter, Pedosphaera, Mucispirillum, and Thermosporothrix were significantly overrepresented in szl1-1. The metabolic pathways, PWY-5304, PWY-5419, PWY-5415, and GLUCARDEG-PWY in szl1-1 were significantly stronger than those in WT. The flowering time of WT and szl1-1 correlated positively with Thermosporothrix and Rhizobacter but negatively with Burkholderia, Flavisolibactor, and Mucilaginibacter. The associations between bacteria and flowering time were identical to those between (-)-loliolide and bacteria. Therefore, the flowering time of Arabidopsis may be mediated by rhizosphere bacteria with root-secreted chemical signals.

Automated summary

This study reveals the influence of root-secreted signaling molecules and rhizosphere bacteria on the flowering time of Arabidopsis. The root-secreted small molecule signal (-)-loliolide can regulate the flowering time of Arabidopsis and affect the bacterial communities in the rhizosphere and soil. The carotenoid-deficient Arabidopsis mutant szl1-1, which does not secrete (-)-loliolide, exhibits an early flowering time and a different rhizosphere and soil bacterial community compared to the wild-type Arabidopsis.