Calcium Signaling Is Suppressed inMagnaporthe oryzaeConidia byBacillus cereusHS24

Abstract

Rice yield is greatly reduced owing to rice blast, a polycyclic fungal disease caused by the ascomycete Magnaporthe oryzae. Previously, Bacillus cereus HS24, isolated from a rice farm, showed a strong antimicrobial effect toward M. oryzae. To better exploit it as a biocontrol agent, HS24 was studied for the mechanism that it uses to suppress rice blast. Conidium germination in M. oryzae was significantly inhibited by HS24, whereby inhibition reached 97.8% at the concentration of 107 CFU/ml. The transcription levels of Ca2+/calmodulin-dependent protein kinase II, PMC1, and CCH1, key genes involved in the M. oryzae Ca2+ signaling pathway, were significantly decreased in HS24-treated conidia at high concentration. The treatment of M. oryzae with the corresponding Ca2+ signaling pathway inhibitors KN-93, verapamil, and cyclopiazonic acid significantly reduced conidium germination. This inhibitory effect was found to be concentration dependent, similar to the HS24 treatment. We also found that HS24 was able to decrease the intracellular free Ca2+ concentration in M. oryzae conidia significantly. The addition of exogenous Ca2+ did not diminish the inhibitory effect of HS24 on the reduction of intracellular free Ca2+ concentration and the level of conidium germination. In conclusion, B. cereus HS24 at high concentration prevents extracellular Ca2+ from entering the conidia in M. oryzae, causes a significant reduction of intracellular free Ca2+ concentration, and results in the inhibition of conidium germination.

Screening and Application of Bacillus Strains Isolated from Nonrhizospheric Rice Soil for the Biocontrol of Rice Blast

“…Bacillus species can indirectly inhibit phytopathogens through biocontrol strategies including the repossession of pathogenic iron by siderophores, the production of hydrolytic enzymes to degrade pathogenic cell walls, and the production of antibiotics to interfere with pathogenic respiration (Ahmad et al, 2017;Li et al, 2014;Li et al, 2017;Qi et al, 2017;Zhang and Sun, 2018). Huang et al (2020) isolated B. cereus HS24 from a rice farm; B. cereus HS24 could significantly reduce conidium germination by interfering with the M. oryzae Ca 2+ signaling pathway. SEM analysis revealed that B. amyloliquefaciens S170 and B. pumilus S9 degraded the hyphae and conidial cell walls of M. oryzae P131.…”

Efficacy of Plant Growth-Promoting Bacteria Bacillus cereus YN917 for Biocontrol of Rice Blast

“…Microbial fungicides can not only reduce the occurrence of diseases, but also maintain the ecological equilibrium ( Zhou et al, 2019 ). Previous studies have reported that Bacillus cereus strains exhibited antifungal activity against M. oryzae in vitro or in vivo , which is expected to be developed as fungicides to control rice blast, such as the B. cereus HS24 ( Huang et al, 2020 ), B. cereus AR156 ( Jiang et al, 2020 ), and B. cereus KF822666 ( Hassan et al, 2019 ). These studies provided a background for the development of biocides.…”

Characterization and Inhibitory Effects of an Antifungal Protein from the Bacillus cereus Strain YN917

“…The Bacisubin protein, produced by B. subtilis B-916 (Liu et al 2007) can cause the R. solani mycelia to enlarge and rupture, and the crude antifungal protein RY3 produced by B. amyloliquefacens RY3 can inhibit the germination of P. digitatum spores (Chen et al 2013). Finally, the protein produced by B. cereus HS24, can significantly inhibit conidium germination and mycelial growth in M. oryzae (Huang et al 2019).…”