Elucidating the role of the phenylacetic acid metabolic complex in the pathogenic activity of Rhizoctonia solani anastomosis group 3

Abstract

The soil fungus Rhizoctonia solani produces phytotoxic phenylacetic acid (PAA) and hydroxy (OH-) and methoxy (MeO-) derivatives of PAA. However, limited information is available on the specific role that these compounds play in the development of Rhizoctonia disease symptoms and concentration(s) required to induce a host response. Reports that PAA inhibits the growth of R. solani conflict with the established ability of the fungus to produce and metabolize PAA. Experiments were conducted to clarify the role of the PAA metabolic complex in Rhizoctonia disease. In this study the concentration of PAA and derivatives required to induce tomato root necrosis and stem canker, in the absence of the fungus, and the concentration that inhibits mycelial growth of R. solani were determined. The effect of exogenous PAA and derivatives of PAA on tomato seedling growth also was investigated. Growth of tomato seedlings in medium containing 0.1-7.5 mM PAA and derivatives induced necrosis of up to 85% of root system. Canker development resulted from injection of tomato seedling stems with 7.5 mM PAA, 3-OH-PAA, or 3-MeO-PAA. PAA in the growth medium reduced R. solani biomass, with 50% reduction observed at 7.5 mM. PAA, and derivatives were quantified from the culture medium of 14 isolates of R. solani belonging to three distinct anastomosis groups by GC-MS. The quantities ranged from below the limit of detection to 678 nM, below the concentrations experimentally determined to be phytotoxic. Correlation analyses revealed that isolates of R. solani that produced high PAA and derivatives in vitro also caused high mortality on tomato seedlings. The results of this investigation add to the body of evidence that the PAA metabolic complex is involved in Rhizoctonia disease development but do not indicate that production of these compounds is the primary or the only determinant of pathogenicity.

3-Methylthiopropionic Acid of Rhizoctonia solani AG-3 and Its Role in the Pathogenicity of the Fungus

“…The activity of MTPA was relatively stable in the range of pH levels 3.5–7.0 and decreased significantly beyond these limits. The minimum activity was observed above pH 7.0 contrary to Bartz et al (2012) who observed that the optimal pH for the activity of phenylacetic acid (PAA) from R. solani infected tomato plant was 5.5. This suggests that the activity of MTPA may be due to their acidic nature.…”

Genes of the de novo and Salvage Biosynthesis Pathways of Vitamin B6 are Regulated under Oxidative Stress in the Plant Pathogen Rhizoctonia solani

“…To obtain further insights into the putative activities of vitamin B6, we also assessed whether the relative transcripts abundance of RsolPDX1, RsolPDX2 , and RsolPLR are regulated by PAA, an antimicrobial and antioxidant compound produced by R. solani AG3 (Bartz et al, 2012 ). The three genes were mostly down-regulated in the range of 5.0–1.5 fold at 24 and 72 HPT, respectively (Figures 7C,F,I ).…”

“…No amendment was added to the half-strength PDB media in the control plates. Oxidant sensitivity and effective concentrations (EC 50 ) for H 2 O 2 and paraquat were determined by obtaining dose-response curves and the concentration which resulted in near 50% inhibition of R. solani growth at 72 hours post treatment (HPT) (Wang et al, 2011 ), whereas the concentration of applied PAA was selected based on previous reports (Bartz et al, 2012 ). The vitamin B6 vitamers were chosen based on optimized concentrations that do not inhibit the growth of R. solani .…”

UPLC-QTOF-MS metabolomics analysis revealed the contributions of metabolites to the pathogenesis of Rhizoctonia solani strain AG-1-IA

“…Agar plugs from starter cultures were placed on PDA in Petri dishes (9 cm in diameters) and grown at 28°C in the dark. Based on the results of previous research, the concentration of PAA used for this study was set as 7.34 mM [ 23 ]. The PAA solution was prepared by dissolving 0.1 g of PAA (chemically pure) in 100 ml of distilled water and was filtrated through 0.22 μm filters.…”