AUTHOR=Tran Trang Minh , Ameye Maarten , Devlieghere Frank , De Saeger Sarah , Eeckhout Mia , Audenaert Kris 

TITLE=Streptomyces Strains Promote Plant Growth and Induce Resistance Against Fusarium verticillioides via Transient Regulation of Auxin Signaling and Archetypal Defense Pathways in Maize Plants

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.755733

DOI=10.3389/fpls.2021.755733

ISSN=1664-462X

ABSTRACT=<p>Driven by climate change, <italic>Fusarium</italic> ear rot (FER) caused by <italic>Fusarium verticillioides</italic> occurs frequently in maize worldwide. In parallel, legislative regulations and increasing environmental awareness have spurred research on alternative FER biocontrol strategies. A promising group of bacterial control agents is <italic>Streptomyces</italic> species due to their metabolic versatility. However, insights into the molecular modes of action of these biocontrol agents are often lacking. This study aims at unraveling the biocontrol efficacy of <italic>Streptomyces</italic> rhizobacterial strains against <italic>F. verticillioides</italic>. We first assessed the direct antagonism of four <italic>Streptomyces</italic> strains ST02, ST03, ST07, and ST08. Then, a profile of 16 genes associated with intrinsic plant defense signaling was assessed in maize plants. Both <italic>in vitro</italic> and <italic>in vivo</italic> data showed that the biocontrol strain ST03 perfectly suppressed the growth of <italic>F. verticillioides</italic>. High inhibition efficacy was also observed for extracellular compounds in the supernatant secreted by this strain. Especially, for maize cobs, the biocontrol strain ST03 not only inhibited the proliferation of <italic>F. verticillioides</italic> but also significantly repressed fungal fumonisin production 7 days after inoculation. On maize plants, the direct antagonism was confirmed by a significant reduction of the fungal DNA level in soils when co-applied with <italic>F. verticillioides</italic> and strain ST03. In terms of its action on plants, strain ST03 induced downregulation of auxin responsive genes (<italic>AUX1</italic>, <italic>ARF1</italic>, and <italic>ARF2</italic>) and gibberellic acid (GA)-related gene <italic>AN1</italic> even in the absence of <italic>F. verticillioides</italic> at early time points. In leaves, the biocontrol strain induced the expression of genes related to salicylic acid (SA), and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA)-mediated pathways, and pathogenesis-related proteins in the presence or absence of the pathogen. Interestingly, the biocontrol strain significantly promoted plant growth even in the presence of <italic>F. verticillioides</italic>. All of which demonstrated that the <italic>Streptomyces</italic> strain ST03 is a promising FER biocontrol and a growth-promoting candidate.</p>