Hormonal regulations in soluble and cell-wall bound phenolic accumulation in two cultivars of <i>Brassica napus</i> contrasting susceptibility to <i>Xanthomonas campestris</i> pv. <i>campestris</i>

Abstract

Xanthomonas campestris pv. campestris (Xcc)-responsive soluble and cell wall-bound hydroxycinnamic acids (HAs) and flavonoids accumulation in relation to hormonal changes in two Brassica napus cultivars contrasting disease susceptibility were interpreted with regard to the disease resistance. At 14-day post inoculation with Xcc, disease resistance in cv. Capitol was distinguished by an accumulation of specific (HAs) and flavonoids particularly in cell-wall bound form, and was characterized by higher endogenous jasmonic acid (JA) resulting in a decrease of JA-based balance with other hormones, as well as enhanced expression of JA signaling that was concurrently based on upregulation of PAP1 (production of anthocyanin pigment 1), MYB transcription factor, and phenylpropanoid biosynthetic genes. Fourier transform infrared spectra confirmed higher amounts of esterified phenolic acids in cv. Capitol. These results indicate that enhanced JA levels and signaling in resistant cultivar was associated with a higher accumulation of HAs and flavonoids, particularly in the cell wall-bound form, and vice versa in the susceptible cultivar (cv. Mosa) with enhanced SA-, ABA-, and CK-levels and signaling. Thus the JA-mediated phenolic metabolites accumulation is an important feature for the management and breeding program to develop disease-resistant B. napus cultivar.