2-Aminobenzoic acid of Bacillus sp. BS107 as an ISR determinant against Pectobacterium carotovorum subsp. carotovotrum SCC1 in tobacco

Root drench-treatment of tobacco seedlings with Bacillus sp. BS107 (BS107) suppressed disease development caused by the pathogen Pectobacterium carotovorum subsp. carotovotrum SCC1 (SCC1). A determinant of BS107 involved in induced systemic resistance (ISR) against SCC1 was isolated from cell-free culture. ISR bioassay-guided isolation was involved in determining active fractions during chromatography. Mass spectrometry and NMR analyses of the isolated metabolite identified 2-aminobenzoic acid (2-AB) as a main ISR determinant. 2-AB at 2.3 mM suppressed significantly disease development and exhibited no direct contact inhibition of pathogen. Reverse Transcriptase (RT)-PCR analyses of tobacco leaves revealed up-regulation of the induced resistance marker genes such as PR1a, PR1c, PR2 and PR4 by application of 2-AB on the root. Among aminobenzoic acids tested, 2- and 4-aminobenzoic acids showed ISR activity against soft-rot pathogen, but 3-aminobenzoic acid did not. This is the first report that 2-AB exhibits the ISR against SCC1in tobacco. BS107 can play a role in promoting plant defences by secretion of bacterial determinants including 2-AB for elicitation of ISR.