## 4 Discussion  
Plant growth-promoting biocontrol agents provide sustainable strategies for agriculture to adapt to abiotic and biotic stress. These agents modulate plant development and growth directly and indirectly. _Streptomyces pratensis_ S10 inhibits fungal mycelial growth, conidiation, conidial germination, and perithecia production and reduces DON content in _F. graminearum_[24; 35]. S10 produces a compound, venturicidin A, which significantly inhibits _F. graminearum_[36]. However, the effects of S10 on wheat plant growth and induced wheat plant resistance have not been investigated. In this study, we observed that root drenching with S10 alleviated the stress of _F. graminearum_ in wheat seedlings by triggering the host defense mechanisms. More importantly, S10 greatly improved plant growth and development, contributing to alleviating pathogen stress in the plants. Multiple BCAs possess the features of enhancing plant growth and promoting the acquisition and utilization of mineral nutrients, which contributes to disease inhibition [13; 37]. In this study, S10 was confirmed to efficiently improve wheat plant growth in a growth chamber (Figure 2). The excellent efficiency of S10 in improving wheat plant development may result from the production of plant growth-promoting compounds and relevant genes in the genome (Tables S2-S5). A previous report demonstrated that the production of IAA and ACC deaminase is extremely vital for the growth-promoting abilities of _Streptomyces_ spp. [16]. S10 generated IAA or IAA-like compounds (Figure 1), which is consistent with the existence of three IAA biosynthesis pathways in its chromosome (Supplementary Table S2). IAA is a major character in plant growth-promoting BCAs [36], which improve the development of plant roots by boosting the elongation and proliferation of root cells [38]. S10 produces ACC deaminase in vitro (Figure 1) and harbors a gene related to the synthesis of ACC deaminase (Table S2). ACC deaminase can decompose ACC (the direct precursor of ethylene), consequently suppressing ethylene biosynthesis in plants to enhance the capacity of plants to survive in unfavorable circumstances. Importantly, ACC deaminase was shown to synergistically interact with IAA and promote plant growth by regulating ethylene levels, one of the most important modulatory hormones of plant development [38; 39]. S10 also displayed other plant growth promotion activities, comprising the production of HCN and siderophores, nitrogen fixation, and phosphate solubilization (Figure 1). Siderophore compounds facilitate plant nutrient absorption, acting as a direct mechanism in enhancing plant development, and they are also one of the most important mechanisms in inhibiting the plant pathogen by iron competition [8; 40]. Furthermore, antiSMASH analysis found that S10 showed a prominent potential to biosynthesize several types of siderophores and a cluster involved in siderophores [24]. Siderophore compounds (catecholty type siderophores, hydroxamate-type siderophores, and mixed-type siderophores) produced by _Streptomyces_ spp. can facilitate iron acquisition in the plant rhizosphere or prevent phytopathogens by reducing iron assimilation [41; 42]. Phosphate deficiency is one of the restricted elements in crop yields. _S. griseus_-related strains with the ability to solubilize phosphate were demonstrated to alleviate the stress of _Pythium ultimum_ in wheat [43]. _Streptomyces_ spp. also can alleviate fungal disease stress in plants by inducing host plant resistance pathways. S10 was demonstrated to induce wheat seedling resistance to suppress _F. graminearum_ infection (Figure 3). Previous studies have documented that _Streptomyces_ spp. induce the plant defense response by the production of antioxidant enzymes, callose deposition, and ROS accumulation [8; 10; 30]. Callose deposition and ROS accumulation are hallmark events of plant early defense responses [44].