The Mechanism Underlying the Growth Stimulation of Rice Plants by Burkholderia cepacia

Oryza sativa L. is renowned for its exceptional plant productivity and resilience to some stresses. This study focused on the mechanism underlying how Burkholderia cepacia, a bacteria that produces high levels of auxin hormone, promotes the growth of rice plants. The bacterial suspension at 10 and 20 mL/L was incubated with plants. The parameters were measured after 14 and 42 days of culturing IR64 seedlings on a medium supplemented with filtered bacterial suspension either in vitro or in the growth chamber. The study demonstrated that 20 mL/L of bacterial suspension resulted in significant improvements in the length and biomass of rice plants. Moreover, plants supplemented with 20 mL/L accumulated higher concentrations of the endogenous auxin hormone indole-3-acetic acid (IAA) and enhanced antioxidant activity compared to the control. Notably, the qRT-PCR analysis revealed distinct differences in gene expression patterns responding to bacteria. The root plants treated with bacterial suspensions significantly upregulated the expression of genes encoding catalase antioxidant enzymes, with fold increases of approximately 3.7 and 1.5 times, respectively, relative to the control. Furthermore, the expression of salicylic acid hydroxylase gene was markedly elevated in the shoots at both bacterial concentrations whereas allene oxide cyclase gene was activated only in shoots of plants supplemented with 10 mL/L. Finally, plants supplemented with bacterial suspension had earlier flowering than the control. These findings provide a comprehensive understanding of the mechanisms by which Burkholderia cepacia strain 205 enhances rice plant growth and offer a sustainable alternative method to reduce agricultural inputs and synthetic auxins while enhancing productivity.