Comparative transcriptome analysis reveals the mechanism of cross-protection against Verticillium wilt conferred on sunflower by hypovirulent strain Gibellulopsis nigrescens Vn-1

Background: Hypovirulent fungal strain Gibellulopsis nigrescens Vn-1 cross-protects sunflower against Verticillium wilt. To discover the mechanism of cross-protection by this hypovirulent strain, we analyzed defense enzyme activities and transcriptomes of root samples infected with virulent and hypovirulent strains. Results: : Defense enzyme activities increased after inoculation, with the highest levels observed 24 h post-inoculation. At the same time, defense enzyme gene expressions were upregulated, and H 2 O 2 accumulation decreased. A comparative transcriptome analysis revealed that three specific oxidoreductase-related GO terms were significantly enriched in the Vn-1 group compared with the control. In addition, 33 resistance genes and 160 susceptibility genes were predicted. Seven transcription factors (TFs), two phytohormone response factors, two E3 ubiquitin-protein ligases, two CCR4-associated factor 1 proteins, and two predicted leucine repeat rich (LRR) receptors were found to contribute to the conferral of resistance on sunflower. Conclusions: : According to our results, hypovirulent strain G. nigrescens Vn-1 can reduce levels of reactive oxygen species in sunflower induced by infection with virulent strains such as V. dahliae V33 by regulating HaCAT expression. Furthermore, multiple resistance-related TFs, phytohormones, and receptors contribute to the formation of specific resistance against virulent strain V. dahliae V33.