In recent years salicylic acid (SA) has been the focus of intensive research due to its function as an endogenous signal mediating local and systemic plant defence responses against pathogens. It has also been found that SA plays a role during the plant response to abiotic stresses such as drought, chilling, heavy metal toxicity, heat, and osmotic stress. In this sense, SA appears to be, just like in mammals, an 'effective therapeutic agent' for plants. Besides this function during biotic and abiotic stress, SA plays a crucial role in the regulation of physiological and biochemical processes during the entire lifespan of the plant. The discovery of its targets and the understanding of its molecular modes of action in physiological processes could help in the dissection of the complex SA signalling network, confirming its important role in both plant health and disease. Here, the evidence that supports the role of SA during plant growth and development is reviewed by comparing experiments performed by exogenous application of SA with analysis of genotypes affected by SA levels and/or perception.

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A water-soluble compound related to zearalenone was isolated from a culture of Fusarium graminearum 30 grown in rice. The structure of the novel metabolite was determined to be zearalenone-4-sulfate on the basis of fast-atom-bombardment mass spectrometry, proton nuclear magnetic resonance, UV spectroscopy, and by chemical and enzymatic reactions. Strains representing Fusarium equiseti, Fusarium sambucinum, and Fusarium roseum produced the sulfate conjugate as well. In the rat uterus enlargement bioassay, the metabolite or its hydrolysis product was found to retain the estrogenic activity characteristic of zearalenone. Natural occurrence of this novel metabolite might be significant because analytical methods devised for zearalenone in grain cannot detect the conjugate but the conjugate retains the biological properties of the mycotoxin when ingested by animals.

Fumonisins are mycotoxins produced by Fusarium verticillioides (Sacc. Nirenberg) in maize (Zea mays L.), a staple crop in Mexico. In this study, we report the isolation and identification of 67 Fusarium strains isolated from maize kernels collected in Northwest and Central Mexico. The strains were characterized regarding fumonisin B(1) production and the presence of the FUM1 gene. F. verticillioides was the predominant species isolated in both geographic regions, but the isolates from Northwest Mexico produced higher levels of fumonisin. A polymerase chain reaction (PCR)-based method, to detect a region of the FUM1 gene involved in fumonisin biosynthesis, was developed and employed to detect mycotoxigenic fungi in pure culture and in contaminated maize. The presence of the FUM1 gene was associated with fumonisin production in most isolates, except seven that did not synthesize fumonisin but contained the gene in their genome. The PCR method allowed the direct detection of fungal contamination in ground corn and could be employed to screen for the presence of potential mycotoxigenic fusaria.

The field of plant sphingolipid biology has evolved in recent years. Sphingolipids are abundant in cell membranes, and genetic analyses revealed essential roles for these lipids in plant growth, development, and responses to abiotic and biotic stress. Salicylic acid (SA) is a key signaling molecule that is required for induction of defense-related genes and rapid and localized cell death at the site of pathogen infection (hypersensitive response) during incompatible host–pathogen interactions. Conceivably, while levels of SA rapidly increase upon pathogen infection for defense activation, they must be tightly regulated during plant growth and development in the absence of pathogens. Genetic and biochemical evidence suggest that the sphingolipid intermediates, long-chain sphingoid bases, and ceramides, play a role in regulating SA accumulation in plant cells. However, how signals generated from the perturbation of these key sphingolipid intermediates are transduced into the activation of the SA pathway has long remained to be an interesting open question. At least four types of molecules – MAP kinase 6, reactive oxygen species, free calcium, and nitric oxide – could constitute a mechanistic link between sphingolipid metabolism and SA accumulation and signaling.

Trichoderma species are fungi widely employed as plant-growth-promoting agents and for biological control. Several commercial and laboratory-made solid formulations for mass production of Trichoderma have been reported. In this study, we evaluated a solid kaolin-based formulation to promote the absortion/retention of Trichoderma asperellum in the substrate for growing tomato plants. The unique implementation of this solid formulation resulted in an increased growth of the tomato plants, both in roots and shoots after 40 days of its application. Plants were challenged with two fungal pathogens, Fusarium oxysporum and Botrytis cinerea, and pretreatment with T. asperellum resulted in less severe wilting and stunting symptoms than non-treated plants. Treatment with T. asperellum formulation inhibited Reactive Oxygen Species (ROS) production in response to the pathogens in comparison to plants that were only challenged with both pathogens. These results suggest that decrease in ROS levels contribute to the protective effects exerted by T. asperellum in tomato.

Summary Nucleotide biosynthesis proceeds through a de novo pathway and a salvage route. In the salvage route, free bases and/or nucleosides are recycled to generate the corresponding nucleotides. Thymidine kinase (TK) is the first enzyme in the salvage pathway to recycle thymidine nucleosides as it phosphorylates thymidine to yield thymidine monophosphate. The Arabidopsis genome contains two TK genes −TK1a and TK1b− that show similar expression patterns during development. In this work, we studied the respective roles of the two genes during early development and in response to genotoxic agents targeting the organellar or the nuclear genome. We found that the pyrimidine salvage pathway is crucial for chloroplast development and genome replication, as well as for the maintenance of its integrity, and is thus likely to play a crucial role during the transition from heterotrophy to autotrophy after germination. Interestingly, defects in TK activity could be partially compensated by supplementation of the medium with sugar, and this effect resulted from both the availability of a carbon source and the activation of the nucleotide de novo synthesis pathway, providing evidence for a compensation mechanism between two routes of nucleotide biosynthesis that depend on nutrient availability. Finally, we found differential roles of the TK1a and TK1b genes during the plant response to genotoxic stress, suggesting that different pools of nucleotides exist within the cells and are required to respond to different types of DNA damage. Altogether, our results highlight the importance of the pyrimidine salvage pathway, both during plant development and in response to genotoxic stress.

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