Volatile organic compounds from Bacillus sp. PAR690 Promote plant growth by regulating photosynthesis and nitrogen metabolism.

Abstract

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.