The Modulation of Leaf Cell‐Wall Composition in <i>Arabidopsis thaliana</i> by the Drought‐Mitigating Rhizobacterium, <i>Bacillus endophyticus</i> <scp>J13</scp>

Plant growth-promoting rhizobacteria (PGPR) are beneficial soil bacteria that reside near plant roots (in the rhizosphere) and support plants in various ways. The specific molecular mechanisms involved in these beneficial interactions are still under scrutiny. In this context, the present study describes the role of Bacillus endophyticus J13, a multiple abiotic-stress-tolerant PGPR, in modulating various components of the leaf cell wall in Arabidopsis thaliana, under well-watered and drought conditions. We have previously reported the positive impact of J13 on drought mitigation in A. thaliana by modulation of soil water content. In the present study, we inoculated A. thaliana roots with J13 under well-watered or water-stressed conditions and analysed the cell wall composition in leaves under the different treatments. We observed an inoculation-specific reduction in lignin content, both under well-watered and water-stressed conditions, while the cellulose content was found to be significantly higher in water-stressed plants inoculated with J13. The expression of genes involved in both the lignin and cellulose biosynthetic pathways was upregulated in water-stressed plants inoculated with J13. J13 inoculation in A. thaliana mutants compromised in cellulose biosynthesis eliminated the beneficial impact of the bacteria, indicating the importance of a functional cellulose biosynthetic pathway in J13-mediated drought tolerance in A. thaliana. J13 inoculation in A. thaliana mutants with altered lignin composition (mutants with higher S lignin) exhibits no beneficial impact by J13, demonstrating the importance of lignin composition towards the plant-growth-promoting activity of J13 in A. thaliana. This study demonstrates that J13 enhances the saccharification efficiency of A. thaliana leaves under dehydration stress by reducing the amount of lignin and elevating the amount of cellulose. Overall, our study suggested that modulation in cell wall composition could be an important mechanism employed by J13 for drought mitigation in A. thaliana, which also positively influences polysaccharide digestibility. Therefore, such a strategy may be used to improve plant immunity and lignocellulosic properties.