In yeast, the stress-responsive protein Whi2 interacts with phosphatase Psr1 to form a complex that regulates cell growth, reproduction, infection, and the stress response. However, the roles of Whi2 and Psr1 in Fusarium graminearum remain unclear. In this study, we identified homologous genes of WHI2 and PSR1 in F. graminearum and evaluated their functions by constructing deletion mutants. By comparing the responses of the mutants to different stressors, we found that FgWHI2 and FgPSR1 were involved in responding to osmotic, cell wall and cell membrane stresses, while also affecting the sexual and asexual reproduction in F. graminearum. Our studies demonstrated that FgWHI2 and FgPSR1 regulate the biosynthesis of ergosterol and the transcriptional level of FgCYP51C, which is a CYP51 paralogues unique to Fusarium species. This study also found that the deoxynivalenol (DON) production of FgWHI2 and FgPSR1 deletion mutants was reduced by ≥ 90% and DON production was positively correlated with the transcriptional levels of FgWHI2 and FgPSR1. In addition, we observed that FgWHI2 and FgPSR1 were involved in regulating the sensitivity of F. graminearum to chlorothalonil, fluazinam, azoxystrobin, phenamacril, and oligomycin. This study revealed the existence of cross-resistance between chlorothalonil and fluazinam. chlorothalonil and fluazinam inhibited DON biosynthesis by suppressing the expression of FgWHI2. Interestingly, the subcellular localization of FgWhi2 and FgPsr1 was significantly altered after treatment with chlorothalonil and fluazinam, with increased co-localization. Collectively, these findings indicate that FgWHI2 and FgPSR1 play crucial roles in stress response mechanisms, reproductive processes, secondary metabolite synthesis, and fungicide sensitivity in F. graminearum.

BACKGROUND:Rice blast, caused by Magnaporthe oryzae, is a destructive disease threatening the production of staple foods worldwide. Quinone outside inhibitors (QoIs) are a group of chemicals exhibiting excellent activity against a majority of plant pathogens, with the disadvantage that pathogens can easily develop resistance to QoIs.RESULTS:Here, we investigated the activity of picoxystrobin against M. oryzae, which showed a great inhibitory effect on 100 strains of M. oryzae with half-maximal effective concentrations (EC50 ) ranging from 0.0251 to 0.1337 μg ml-1 . The EC50 values showed a continuous unimodal distribution that was identical to the normal distribution, suggesting the potency of our study to represent baseline sensitivity. In addition, nine resistant mutants were obtained by exposing M. oryzae to a high dosage of picoxystrobin in the laboratory; all of them showed cross-resistance to the other five QoI fungicides. Although some mutants showed a decreased resistance factor after ten successive cultures on fungicide-free medium, the resistance to picoxystrobin was still inheritable. Amino acid substitution of G143S was detected in eight of nine picoxystrobin-resistant mutants, and G143A was detected in only one of nine mutants. A fitness penalty was found in the mutants carrying G143S rather than G143A.CONCLUSION:Our findings suggested that M. oryzae had a mid to high risk of resistance to picoxystrobin. Considering this, we should be vigilant to the resistance risk and apply picoxystrobin sensibly in the field. © 2022 Society of Chemical Industry.

Spiroplasma melliferum generally parasitizes honeybees and is one of main pathogens causing 'bee creeping disease' in China. Spiroplasma melliferum can be spread through honeybee pollination, which causes severe economic losses to apiculture. The design of this study was based on previous studies that utilized an in vitro bioassay to investigate the effects of S. melliferum CH-1 infection. We identified invasive S. melliferum CH-1 within Apis mellifera using transmission electron microscopy and investigated the immune response of honeybees infected with S. melliferum CH-1 by assaying the cellular immune response of the haemocytes, the plasma level of phenoloxidase activity and the transcript levels of 5 antimicrobial peptides, including the Abaecin, Apidaecin, Defensin 1, Defensin 2, and Hymenoptaecin gene products. The percentage of granulocytes in the haemolymph of infected honeybees was significantly higher than those of the controls during the early phase of infection, but the percentage of plasmatocytes was significantly higher than those of the controls at the fifth day post-infection. The phenoloxidase activity of the infected honeybees reached a maximum at the second day, and then decreased continuously. Moreover, the transcript levels of the 5 evaluated antimicrobial peptide genes were significantly increased during the early phase of infection and all 5 antimicrobial peptides were significantly decreased during the middle phase of infection. During the late phase of infection, only Defensin 2 and Hymenoptaecin showed significantly increased transcription. These results suggest that the honeybee immune responses could be activated by S. melliferum CH-1 during the early phase of infection and that S. melliferum CH-1 is also capable of circumventing the host defensive mechanisms to complete its life cycle within the honeybee during the middle phase of infection.