Endophytic fungi from kale (Brassica oleracea var. acephala) modify roots-glucosinolate profile and promote plant growth in cultivated Brassica species. First description of Pyrenophora gallaeciana

Endophytic fungi of crops can promote plant growth through various mechanisms of action (i.e., improve nutrient uptake and nutrient use efficiency, and produce and modulate plant hormones). The genus Brassica includes important horticultural crops, which have been little studied in their interaction with endophytic fungi. Previously, four endophytic fungi were isolated from kale roots (Brassica oleracea var. acephala), with different benefits for their host, including plant growth promotion, cold tolerance, and induction of resistance to pathogens (Xanthomonas campestris) and pests (Mamestra brassicae). In the present work, the molecular and morphological identification of the four different isolates were carried out, describing them as the species Acrocalymma vagum, Setophoma terrestris, Fusarium oxysporum, and the new species Pyrenophora gallaeciana. In addition, using a representative crop of each Brassica U’s triangle species and various in vitro biochemical tests, the ability of these fungi to promote plant growth was described. In this sense, the four fungi used promoted the growth of B. rapa, B. napus, B. nigra, B. juncea, and B. carinata, possibly due to the production of auxins, siderophores, P solubilization or cellulase, xylanase or amylase activity. Finally, the differences in root colonization between the four endophytic fungi and two pathogens (Leptosphaeria maculans and Sclerotinia sclerotiorum) and the root glucosinolate profile were studied, at different times. In this way, how the presence of progoitrin in the roots reduces their colonization by endophytic and pathogenic fungi was determined, while the possible hydrolysis of sinigrin to fungicidal products controls the colonization of endophytic fungi, but not of pathogens.

PGPBS, a mitogen-activated protein kinase kinase, is required for vegetative differentiation, cell wall integrity, and pathogenicity of the barley leaf stripe fungus Pyrenophora graminea

The high-osmolarity glycerol (HOG) signaling pathway regulates the adaptation of fungi to environmental stressors. The mitogen-activated protein kinase kinase (MAPKK) PBS2 of Saccharomyces cerevisiae serves as a scaffold protein in the HOG pathway. We characterized the pgpbs gene of Pyrenophora graminea, which encodes a MAPKK that is 56% orthologous to PBS2 of S. cerevisiae. A cloning technique based on homology was applied to amplify the pgpbs gene. Specific silent mutations then were generated in pgpbs. We evaluated the potential roles of PGPBS in the osmotic response, vegetative differentiation, cell wall integrity, drug resistance, and pathogenicity. Our findings indicated that the pgpbs coding region comprises 2075 base pairs and encodes a protein of 676 amino acids. Mutants deficient in pgpbs expression had significant reductions in vegetative growth and were sensitive to calcofluor white (CFW), an inhibitor of cell wall synthesis. Mutants also lost pathogenicity and were sensitive to an osmotic stress-inducing medium containing NaCl and sorbitol. Moreover, mutants had increased resistance to the dicarboximide fungicide iprodione and the triazole fungicide tebuconazole. These findings suggest that pgpbs is involved in the osmotic and ionic stress responses, vegetative differentiation, cell wall integrity, virulence, and tolerance to iprodione and tebuconazole. We expect that our findings will help elucidate the pathogenesis of barley leaf stripe and will inform strategies for breeding resistance to this disease.