## 3 Results
### Transcriptomic Analysis of BF06 VOCs-Regulated Gene Profiles  
To decipher the mechanisms underlying the release of VOCs by BF06 regulated plant growth, whole genome expression profiling of Arabidopsis plants was performed using RNA-Seq. For this purpose, seven-day-old _Arabidopsis_ plants were grown on 1/2 MS medium for 10 days with or without exposure to BF06 VOCs. Changes in gene transcription were examined by comparing the control and VOCs-exposed plants. To evaluate the accuracy of RNA-Seq analyses, the original sequences were firstly filtered to ensure the quality of reads. The RNA-Seq generated about 35.5 million raw reads, and approximately 98% of the raw reads were mapped to the _Arabidopsis_ genome. The RNA-Seq analyses further revealed that 761 genes were differentially expressed in the VOCs-exposed plants. Compared with the controls, 335 genes were upregulated and 426 genes were downregulated in the VOCs-exposed plants (Table S3). To further explore the biological processes in _Arabidopsis_ plants that were mediated by VOCs released by BF06, gene ontology (GO) analysis was applied to the above DEGs, and enrichment analysis was carried out by using an FDR-adjusted \(p\) value < 0.05 as the cutoff. The GO enrichment analysis revealed the major functional categories including biological processes (BP), cellular components (CC), and molecular function (MF) in the upregulated (Ur) and downregulated (Dr) DEGs. The most overrepresented GO terms in the BP domain of Ur DEGs related to some important metabolic pathways such as amino acid transport, Fe homeostasis, response to Fe,  
Figure 2: The release of VOCs by BF06 increased chlorophyll content and photosynthetic efficiency in _Arabidopsis_. After 10 days of exposure to microbial VOCs, we examined chlorophyll content (**A**); and photosynthetic parameters including photosynthetic rate (**B**); \(Fv/Fm\) (**C**); \(\Phi\)PSII (**D**); and NPQ (**E**) in plants. Different letters represent a significant difference between the control and VOCs-exposed plants at \(p<0.05\).  
and sulfate transport (Figure 3). Furthermore, the most overrepresented categories in the BP domain of Dr DEGs were closely associated with the abscisic acid (ABA)-related pathways including response to ABA, response to various stresses such as water deprivation, cold, salt and wounding, and glutathione, hydrogen peroxide, and toxin catabolic processes (Figure S1).  
Plant roots can secrete abundant metabolites such as amino acids, sugars and organic acids, which serve as a carbon source for most soil-borne bacteria [2; 4]. Herein, BF06 VOCs sufficiently activated the expression of some genes encoding amino acid transporters (Table S4), suggesting that soil microbes could release VOCs to induce root exudates such as amino acids for attracting them colonizing in the rhizosphere, which was not required for physical contact with host plants. We also found that BF06 VOCs markedly upregulated some genes associated with the response of plants to Fe and its homeostasis (Table S4). Recent studies have indicated that Fe deficiency is the major limiting factor for the rate of photosynthesis, and the enhanced ability of plants to absorb Fe is conducive to elevating photosynthesis [21; 22]. As mentioned above, the VOCs-exposed plants exhibited higher photosynthetic efficiency compared with the controls. Thus, plant Fe acquisition was positively regulated by the release of VOCs by BF06. In addition, the transcription of several sulfate transporter genes was significantly increased in the VOCs-exposed plants compared with the controls (Table S4). These sulfate transporter genes have been demonstrated to play essential roles in Se assimilation in _Arabidopsis_ plants [51; 52; 53; 54]. Thus, the VOCs-induced expression of sulfate transporter genes might participate in the regulation of Se accumulation in plants.