Isolation and selection of autochthonous strains of Trichoderma spp. with inhibitory activity against Sporisorium reilianum.

Head smut is a worldwide disease caused by the fungus Sporisorium reilianum. In Mexico, this phytosanitary problem has been described in the central part of the country, specifically in the Mezquital Valley in the state of Hidalgo, where this basidiomycete causes significant economic losses. In this work, seven strains of Trichoderma spp. were isolated from corn rhizospheres collected from crops in the affected zone. The isolates were identified as Trichoderma asperellum MH1, T. asperellum T4H1, T. harzianum T1H1, T. harzianum T1H3, T. atrobrunneum T1H2, T. tomentosum T2H4, and T. brevicompactum T3H1. All strains showed the ability to grow on the phytopathogen but with distinct degrees of mycoparasitism. SEM observations demonstrated the ability of T. asperellum T4H1 to invade the S. reilianum yeast growth. All the strains produced volatile compounds with antifungal activity. With the exception of T. asperellum MH1, all strains inhibited the development of the pathogen by means of non-volatile compounds. Production of the extracellular enzymes (lipase, cellulase, chitinase, protease, and laccase) was evaluated, with most strains presenting high lipolytic activity and low proteolytic activity. The production of cellulase and chitinase was observed only in five strains. Laccase production was found in three isolates. Evaluations at the greenhouse of the sequential application of three mixtures of the isolates were conducted in a greenhouse; findings showed that the phytopathogen was not detected by specific PCR in the plants that received the treatment.

ß-Xylosidase SRBX1 Activity from Sporisorium reilianum and Its Synergism with Xylanase SRXL1 in Xylose Release from Corn Hemicellulose.

Sposisorium reilianum is the causal agent of corn ear smut disease. Eleven genes have been identified in its genome that code for enzymes that could constitute its hemicellulosic system, three of which have been associated with two Endo-ß-1,4-xylanases and one with α-L-arabinofuranosidase activity. In this study, the native protein extracellular with ß-xylosidase activity, called SRBX1, produced by this basidiomycete was analyzed by performing production kinetics and its subsequent purification by gel filtration. The enzyme was characterized biochemically and sequenced. Finally, its synergism with Xylanase SRXL1 was determined. Its activity was higher in a medium with corn hemicellulose and glucose as carbon sources. The purified protein was a monomer associated with the sr16700 gene, with a molecular weight of 117 kDa and optimal activity at 60 °C in a pH range of 4-7, which had the ability to hydrolyze the ρ-nitrophenyl ß-D-xylanopyranoside and ρ-Nitrophenyl α-L-arabinofuranoside substrates. Its activity was strongly inhibited by silver ions and presented Km and Vmax values of 2.5 mM and 0.2 µmol/min/mg, respectively, using ρ-nitrophenyl ß-D-xylanopyranoside as a substrate. The enzyme degrades corn hemicellulose and birch xylan in combination and in sequential synergism with the xylanase SRXL1.

Analysis of gene expression profiles in response to Sporisorium reilianum f. sp. zeae in maize (Zea mays L.)

Background Head smut of maize, which is caused by Sporisorium reilianum f. sp. zeae (Kühn), is a serious disease in maize. In order to reveal the molecular mechanism of the resistance to head smut in maize, a microarray containing ~ 14,850 probes was used to monitor the gene expression profiles between a disease resistant near isogenic line (NIL) and a highly susceptible inbred line after S. reilianum was injected with an artificial inoculation method. Results Levels of expression for 3,532 genes accounting for 23.8% of the total probes changed after inoculation. Gene Ontology analysis revealed that the differentially expressed genes participated in physiological and biochemical pathways. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that plant-pathogen interaction, natural killer cell mediated cytotoxicity and benzoxazinoid biosynthesis pathways play important roles in resistance to head smut. Three head smut resistance-related candidate genes, CLAVATA1, bassinosteroid insensitive 1-associated receptor kinase 1 and LOC100217307 with leucine-rich repeat (LRR) conserved domains were identified, each of which is in maize mapping bin 2.09, a region previously shown to include a major QTL for head smut resistance. Furthermore, LOC100217307 was validated by quantitative real-time (qRT)-PCR inferring that this gene may be involved in the resistance to head smut of maize. Conclusions This study provided valuable information for cloning, functional analysis and marker assisted breeding of head smut resistance genes.