Expression of Genes Involving Disease Resistance in Citrus Fruit Induced by Bacillus subtillis Lipopeptides Elicitors and Fungal Pathogen

Abstract

Cyclic lipopeptides (CLPS) obtained from Bacillus subtilis ABS-S14 had ability to activate some important genes, proteins, and metabolites which are involved in plant defensive pathways to stress responses and infection caused by Penicillium digitatum in mandarin fruit. The effects of CLP extract, fengycin, iturin A and surfactin in enhancement of the expression of PAL, LOX, ACS1, ACO, CHI, GLU, POD and PR1 genes in postharvest mandarin fruit were revealed. Also the proteins relating to Ca2+ pathway, ABA signaling pathway, reactive oxygen species pathway, and ubiquitin- proteasome system including energy production for plant resistance were significantly accumulated. During stress responses (non-fungal infection), fengycin activated plant production of a protein that is involved in plant development and the ubiquinone biosynthetic process while iturin A and surfactin were shown to be involved in auxin and abscisic acid modulating signaling pathways. In addition, a comparative elicitor-protein binding assay of each CLP illustrated that iturin A attached to 12-oxophytodienoate reductase 2 that plays role in oxylipin biosynthetic process required for jasmonic acid production led to inducing systemic resistance (ISR). Furthermore, metabolomic analysis revealed that CLPs elicited a high accumulation of some amino acids; aspartic acid, homoserine, threonine, serine, glycine and tryptophan, which are primary metabolites via the metabolism of glycine, serine and threonine, and the secondary metabolites; serotonin and tyramine, which are active in the metabolism of tryptophan and tyrosine, respectively in postharvest mandarin fruit.