Response in barley roots during interaction with Bacillus subtilis and Fusarium graminearum

Abstract

Barley (Hordeum vulgare), one of the main cereals cultivated around the world, is commonly affected by Fusarium head blight, a disease caused by fungal pathogen Fusarium graminearum. Although several control strategies have been developed, the lack of resistant cultivars and the risks of irritation posed by chemical fungicides mean that current efforts focus on biocontrol, a more sustainable and environmentally friendly approach. The aim of this research was to observe the alterations produced by a strain of Bacillus subtilis in the biology of Fusarium graminearum, and whether the response to the fungus was accordingly modified in barley roots. We found that Bacillus subtilis ATCC 6633 caused morphological distortions in Fusarium graminearum macroconidia and modified the mycelium´s lipid content, so that fungal growth was significantly impaired even after exposure to the bacterium had stopped. In barley assays, interaction with the two microorganisms significantly affected the plant in terms of phospholipase A activity, proline synthesis, and the transcription of genes that code lysophosphatidylcholine acyltransferases (HvLPCAT) and phospholipase A (HvPLA), involved in the metabolism of phosphatidylcholine. The accumulation of reactive oxygen species, however, was not modulated. Analysis of other immunity events triggered by pathogen-associated molecular patterns indicated differential expression of the genes that code two key enzymes to synthesize salicylic acid (SA): an isochorismate synthase (ICS) and phenylalanine ammonia-lyase (PAL). Overall, these findings contribute to our understanding of Bacillus subtilis ATCC 6633′s biocontrol potential, with the ultimate aim of improving biocontrol schemes to protect barley from Fusarium disease