Transcriptional and Metabolic Changes Associated to the Infection by Fusarium verticillioides in Maize Inbreds with Contrasting Ear Rot Resistance

et al. (2013) Transcriptional and Metabolic Changes Associated to the Infection by Fusarium verticillioides in Maize Inbreds with Contrasting Ear Rot Resistance. PLoS ONE 8(4): e61580. doi:10.1371/journal.pone.0061580 Transcriptional and Metabolic Changes Associated to the Infection by Fusarium verticillioides in Maize Inbreds with Contrasting Ear Rot Resistance Valeria A. Campos-Bermudez 0 Carolina M. Fauguel 0 Marcos A. Tronconi 0 Paula Casati 0 Daniel A. Presello 0 Carlos S. Andreo 0 M. Lucrecia Alvarez, TGen, United States of America 0 1 Centro de Estudios Fotosinte ticos y Bioqu micos, Facultad de Ciencias Bioqu micas y Farmace uticas, Universidad Nacional de Rosario, Rosario, Argentina, 2 Instituto Nacional de Tecnolog a Agropecuaria , Pergamino , Argentina Fusarium verticillioides causes ear rot and grain mycotoxins in maize (Zea mays L.), which are harmful to human and animal health. Breeding and growing less susceptible plant genotypes is one alternative to reduce these detrimental effects. A better understanding of the resistance mechanisms would facilitate the implementation of strategic molecular agriculture to breeding of resistant germplasm. Our aim was to identify genes and metabolites that may be related to the Fusarium reaction in a resistant (L4637) and a susceptible (L4674) inbred. Gene expression data were obtained from microarray hybridizations in inoculated and non-inoculated kernels from both inbreds. Fungal inoculation did not produce considerable changes in gene expression and metabolites in L4637. Defense-related genes changed in L4674 kernels, responding specifically to the pathogen infection. These results indicate that L4637 resistance may be mainly due to constitutive defense mechanisms preventing fungal infection. These mechanisms seem to be poorly expressed in L4674; and despite the inoculation activate a defense response; this is not enough to prevent the disease progress in this susceptible line. Through this study, a global view of differential genes expressed and metabolites accumulated during resistance and susceptibility to F. verticillioides inoculation has been obtained, giving additional information about the mechanisms and pathways conferring resistance to this important disease in maize. - Funding: This work was supported by grants from Agencia Nacional para la Promoci on Cientfica y Tecnolo gica, ANPCyT (PICT No. 358); Secretara de Ciencia y Tecnica de la Provincia de Santa Fe, SecTei (Project No. 2010-110-11), and Instituto Nacional de Tecnologa Agropecuaria, INTA. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Fusarium verticillioides, (Saccardo) Nirenberg [( = F. moniliforme (Sheldon), teleomorph Gibberella moniliformis (Wineland) ( = G. fujikuroi (Sawada Ito in Ito & Kimura, mating population A)] is the prevalent kernel and ear rotting pathogen in Argentina [1]. This fungus produces yield losses [2] and grain contamination with several mycotoxins, including fumonisins [35]. Fumonisin occurrence in foods and feeds has wide economic implications [6], and the development of management strategies for controlling F. verticilliodes infection and fumonisin contamination are needed to reduce detrimental effects on human and animal health [7]. There is a positive association between visible symptoms caused by F. verticillioides infection and mycotoxin concentration [8], [9]. F. verticillioides infection and fumonisin contamination occur as maize kernels come up to physiological maturity, and increase during the season up to the average harvest date [10], [11]. F. verticillioides enters the ear through the silk channel, spreads within the ear on the silks, and infects isolated single kernels or groups of kernels in localized areas of the ear [12]. After conidia reach maize silks, penetration and colonization occur with a series of biochemical reactions being affected by resistance mechanisms in the host plant. Therefore, developing and using resistant hybrids may prevent both ear rot progress and grain fumonisin contamination. Although genetic variation for resistance to Fusarium ear rot exists among inbred lines and hybrids in field maize [1315], there is no evidence of complete resistance to either ear rot or fumonisin accumulation. High levels of disease resistance were observed in Argentinean landraces [13] that are being used to improve elite germplasm. In part, the difficulty in developing more resistant genotypes is due to the lack of understanding of the factors important to F. verticillioides infection and fumonisin accumulation. Plants defend themselves against pathogen attack by activating a multicomponent defense response. Activation of signal transduction network after pathogen recognition results in a reprogramming of cellular metabolism involving large changes in gene activity [16]. Expressions of a large array of genes whose products are involved in diverse primary and secondary metabolic pathways are rapidly induced or strongly up-regulated [17]. These responses include induction of pathogenesis related (PR) genes like those coding for glucanases and chitinases, production of secondary metabolites or reinforcement of cell walls. The identification of genes controlling resistance to this fungus in ear rot would facilitate their introgression into commercial hybrids. In plant-pathogen interactions, microarray studies provide a more comprehensive understanding of molecular responses in the infection process, allowing the elucidation of mechanisms involved in resistance. The aim of this work was to identify gene transcripts and metabolic host factors that could control plant resistance and susceptibility to F. verticillioides infection in maize. The knowledge accumulated in these studies will serve as fundamental basis to the development of original strategic agriculture. Symptom Severity, Grain Ergosterol and Fumonisin Content For all the experiments, two maize inbreds with contrasting phenotypes were chosen. Inbred L4637 was classified as resistant and L4674 as susceptible according to their field behavior after a fungal inoculation treatment in a previous experiment [14], [18], [19]. F. verticillioides inoculation was carried out through the silk channel, considering that it is the principal entry route of this fungal pathogen. Disease severity, ergosterol and fumonisin contents were tested in the grains to evaluate field responses of the two maize selected lines (Table 1). The resistant inbred exhibited lower disease severity and grain fumonisin accumulation compared to the susceptible one (Table 1). Disease severity only determines the visual damage in grains; therefore, to analyze the fungus content in the sample, we measured ergosterol levels in infected tissues. Ergosterol is a specific component of the fungal membrane and its analysis is (...truncated)