Plants show strong levels of resistance to an extensive range of pathogens on account of root colonization through plant growth-promoting rhizobacteria (PGPR), namely, induced systemic resistance (ISR). Little is known about bacterial determinants and plant signaling pathways that underpin ISR in cereal crops associated with ISR in dicotyledonous plants. The present study evaluates the potential of Pseudomonas spp. QAU-92 using site directed mutagenesis of the pqqC gene to elicit ISR in rice (Oryza sativa L.) against the fungal pathogen Cochliobolus miyabeanus. The comparison between the wild-type strain and the mutant strain for biochemical attributes, in vitro and in vivo antagonistic activity, carbon source utilization assay and in vivo analyses on rice (cv. C-039) revealed the statistically significant role of Pyrroloquinoline Quinone (PQQ) in plant growth promotion. RT-qPCR analysis revealed that the plant recognition of QAU-92 results in the activation of ethylene (ET) and jasmonic acid (JA) pathways and also shows clear differences in resistance against C. miyabeanus disease compared with the pqqC mutants (QAU92-2). The expression of TF 89 (EBP89), a susceptible gene, as well as the pathogenesis-related protein 1a (PR1a) were much higher in the infected control and pqqC mutant plant than in wild type inoculated plants. Hence, this study is the first of the kind that has investigated the expressional analysis of PQQ against antifungal activity, phosphate solubilization and the induced systemic resistance of QAU-92 against C. miyabeanus in rice. Additionally, PQQ genes may act as a key regulator of PR1a/ET cross-talk and its interference with the fungal manipulation of plants. © 2021 Friends Science Publishers
The role of ethylene in rhizobacteria-induced systemic resistance (ISR)