Plant growth-promoting bacteria (PGPB) enhance plant growth through multiple mechanisms; however, the underlying plant molecular response pathways remain insufficiently understood, particularly those mediated by bacterial volatile organic compounds (VOCs). In this study, a Bacillus strain, designated PAR690, capable of producing growth-promoting VOCs, was isolated from the rhizosphere soil of Achnatherum inebrians . Split-plate assays demonstrated that PAR690 significantly increased chlorophyll a/b, carotenoids, and total chlorophyll contents in Arabidopsis , while simultaneously promoting the accumulation of reducing sugars, soluble sugars, and starch. GC/MS analysis revealed that growth-promoting VOCs produced by Bacillus sp. PAR690 include acetoin, 2,3-butanediol, and indole. Transcriptomic analyses revealed that PAR690 significantly upregulated multiple key genes involved in the “Photosynthesis-antenna proteins”, “Photosynthesis, light harvesting”, and “Chlorophyll catabolic process” pathways. In addition, PAR690 downregulated the expression of methyl esterase 16 while upregulating chlorophyllase 1 , thereby maintaining chlorophyll homeostasis under conditions of elevated chlorophyll content. PAR690 also enhanced nitrogen uptake and accumulation by inducing the expression of nitrate transporter 2.1 and nitrate transporter 2.5 . Moreover, PAR690 significantly increased anthocyanin accumulation in Arabidopsis , an effect closely associated with the upregulation of genes related to UDP-glucose: flavonoid 3-O-glucosyltransferase and production of anthocyanin pigment 1 . Collectively, these findings elucidate the potential mechanisms by which Bacillus sp. PAR690 promotes plant growth via VOC-mediated regulation at both physiological and transcriptional levels, providing new insights into PGPB-plant interactions.
Yang et al. (Fri,) studied this question.