ABSTRACT
Pseudomonas putida is widely used as a biocontrol agent, however, mechanisms by which it initiates the plants’ defenseresponse remains obscure. To gain an insight into the molecular changes that occur in plants upon plant growth-promotingrhizobacteria colonization, root transcriptome analysis by using a microarray was performed in rice using P. putida RRF3 (arice rhizosphere isolate). Data analysis revealed a differential regulation of 61 transcripts (48 h post-treatment), of which,majority corresponded to defense response, cell wall modification and secondary metabolism. Seven genes encodingsalicylic acid (SA) responsive pathogenesis-related proteins were up-regulated significantly (fold change ranges from 1 to4), which suggests that RRF3 has a profound impact on a SA-mediated defense signaling mechanism in rice. Investigationsperformed at later stages of RRF3 colonization by real-time polymerase chain reaction and high-performance liquidchromatography (HPLC) analysis confirmed the above results, demonstrating RRF3 as a potent biocontrol agent. Further,the impact of RRF3 colonization on root exudation, in particular, exudation of SA was investigated by HPLC. However,analysis revealed RRF3 to have a negative impact on root exudation of SA. Overall, this study shows that P. putida RRF3immunizes the rice plants by re-organizing the root transcriptome to stimulate plant defense responses (‘priming’), andsimultaneously protects itself from the primed plants by altering the rhizosphere chemical constituents.