A Short-Term Fertilization of the Nitrogen-Fixing Bacterium (NFB) <i>Kosakonia radicincitans</i> GXGL-4A Agent Can Modify the Transcriptome Expression Profiling of Cucumber (<i>Cucumis sativus</i> L.) Roots to Enhance Resistance to Drought

The application of nitrogen-fixing bacterium (NFB) as biofertilizer can greatly reduce or even avoid the environmental pollution caused by the excessive use of chemical nitrogen fertilizer. In this study, four nitrate transporter (NRT) genes (the Csa1G047430, Csa2G416080, Csa3G027720 and Csa5G161290) subcloned from a Chinese cucumber (Cucumis sativus L.) cultivar “Xintaimici” by RT-PCR were subjected to a determination of the relative expression level using fluorescent quantitative RT-PCR (qRT-PCR). The results showed that the expression of Csa3G027720 gene was significantly up-regulated in the root samples treated with liquid soil extract, and similarly Csa1G047430 and Csa3G027720 genes showed a significant up-regulation when treated with the bacterial cells of GXGL-4A. Differential transcriptome analysis of cucumber roots were conducted between the GXGL-4A-treated group and the control group treated with an equal volume of sterile water. A total of 418 differentially expressed genes (DEGs) were detected and categorized into 20 functional groups. Only the KEGG pathway of phenylpropanoid biosynthesis reached a significant level (P-adjust=0.0279) among all the 17 enriched KEGG pathways. Hence, we speculate that the NFB bacterial strain GXGL-4A, as a biological stimulus, promote the phenylpropanoid biosynthesis in cucumber roots after colonization in cucumber rhizosphere. Under drought condition, the rhizosphere electrical conductivities (EC) of the NFB treatment groups were extremely significantly higher than that of the control group, suggesting that the application of NFB significantly enhanced cucumber&#039;s resistance to drought.