Volatile compounds from Gluconacetobacter diazotrophicus PAL5 regulate photosynthesis and protein networks to promote Arabidopsis thaliana growth.

Plant growth-promoting bacteria (PGPB) produce volatile organic compounds (VOCs) that can enhance plant development without requiring physical contact. Gluconacetobacter diazotrophicus PAL5 is a well-known endophytic PGPB, but its ability to emit plant growth-promoting VOCs has not yet been demonstrated. Here, we evaluated the composition and effects of VOCs emitted by G. diazotrophicus PAL5 on growth, photochemical efficiency, and proteomic profile of Arabidopsis thaliana. VOC exposure led to a significant increase in biomass accumulation, with fresh and dry weights increasing by 228.6% and 248.7%, respectively. Proteomic analyses indicated extensive molecular reprogramming, particularly in photosynthesis-related pathways. Chlorophyll fluorescence measurements confirmed enhanced photochemical efficiency, as indicated by increases in photochemical quenching (40.3%) and electron transport rates (54.3%), along with rises in chlorophyll a (30.8%), chlorophyll b (40.1%), and total chlorophyll content (29.1%). Gas chromatography-mass spectrometry identified 18 VOCs, including carboxylic acids, sulfur compounds, alcohols, and terpenes, some of which have known phytostimulatory properties. Moreover, assays using A. thaliana mutant lines revealed that the ethylene signaling pathway (EIN2-5) is involved in the observed growth-promoting effects. Our findings demonstrate that G. diazotrophicus PAL5 promotes plant growth independently of endophytic colonization by modulating photochemical efficiency and proteomic networks through VOC emissions. This study provides new insights into bacterial-plant communication and highlights the potential of G. diazotrophicus VOCs as bio-stimulants for sustainable agriculture.