Abstract
Endophytic fungi are effective in plant growth and development by secreting various kinds of plant hormones and nutrients. However, the cellular and molecular interactions between the endophytic fungi and plant growth-promoting have remained less explored. The present study was designed to explore the effects of the infection and colonization events of Chaetomium globosum strain ND35 on cucumber growth and the expression pattern of some metabolically important genes in development of the cucumber radicle. The results demonstrated that strain ND35 can infect and colonize the outer layers (cortical cells) of cucumber root and form a symbiotic structure with the host cell, similar to a periarbuscular membrane and establish chemical communication with the plant. Through transcriptome analysis, we found the differentially expressed genes (DEGs) caused by strain ND35 were mainly enriched in phenylpropanoid biosynthesis, plant hormone signal transduction, plant-pathogen interaction and photosynthesis. Correspondingly, the contents of reactive oxygen species (ROS), hydrogen peroxide (H2O2), indole-3-acetic acid (IAA), gibberellin (GA), zeatin (ZT), salicylic acid (SA), jasmonic acid (JA) and the activity of phenylalanine ammonia lyase (PAL), 4-coumarate-CoA ligase (4CL), cinnamyl alcohol dehydrogenase (CAD), and peroxidase (POD) in ND35-colonized seedlings were generally higher than those of non-inoculated seedlings. Overall, the infection and colonization events of C. globosum strain ND35 increased cucumber growth through complex regulation of plant hormones biosynthesis and metabolism. Furthermore, although the endophytic fungus strain ND35 produced IAA, GA, ZT, and ergosterol in the fermentation broth, and there are enabled to promote growth of cucumber, it is uncertain whether there are ND35-derived microbial hormones in plants. This study of the interaction between cucumber and strain ND35 contributes to a better understanding of the plant-endophytic fungi interactions, and may help to develop new strategies for crop production.
Highlights
Healthy plants host a large and varied microbial community, the plant microbiota some confer fitness advantages to the plant host, including growth promotion, nutrient uptake, stress tolerance and resistance to pathogens [1]
The radicle length, fresh weight of radicle, dry weight of radicle, plant height, shoot dry weight, and root dry weight of cucumber inoculated with strain ND35 at the concentration of 1 × 106 spores/mL were significantly increased by 66.9%, 449.1%, 239.5%, 14.1%, 16.7%, and 68.1% compared to those of non-inoculated groups, respectively
The growth vigor of seeds on the seedbed soaked with strain ND35 spore suspension (1 × 106 spores/mL) was lower than that in non-inoculated groups in the first 24 h, while exhibited significantly higher growth rate after 48 h compared with the control (Figure 1)
Summary
Healthy plants host a large and varied microbial community, the plant microbiota some confer fitness advantages to the plant host, including growth promotion, nutrient uptake, stress tolerance and resistance to pathogens [1]. It is demonstrated that endophytes can promote plant growth [8,9], enhance biomass production [3,10], and induce plant defense to the biotic and abiotic stresses, such as plant pathogens, drought and salinity [11,12,13,14]. Endophytes’ ability to assist in plant health, and as the biocontrol agent of plant diseases have been used to reduce the ecological and public health impacts caused by the overuse of chemicals and the emergence of fungicide resistance [2].
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