Abstract
Metal contaminated soils are increasing worldwide. Metal-tolerant plants growing on metalliferous soils are fascinating genetic and microbial resources. Seeds can vertically transmit endophytic microorganisms that can assist next generations to cope with environmental stresses, through yet poorly understood mechanisms. The aims of this study were to identify the core seed endophyte microbiome of the pioneer metallophyte Crotalaria pumila throughout three generations, and to better understand the plant colonisation of the seed endophyte Methylobacterium sp. Cp3. Strain Cp3 was detected in C. pumila seeds across three successive generations and showed the most dominant community member. When inoculated in the soil at the time of flowering, strain Cp3 migrated from soil to seeds. Using confocal microscopy, Cp3-mCherry was demonstrated to colonise the root cortex cells and xylem vessels of the stem under metal stress. Moreover, strain Cp3 showed genetic and in planta potential to promote seed germination and seedling development. We revealed, for the first time, that the seed microbiome of a pioneer plant growing in its natural environment, and the colonisation behaviour of an important plant growth promoting systemic seed endophyte. Future characterization of seed microbiota will lead to a better understanding of their functional contribution and the potential use for seed-fortification applications.
Highlights
Metal contaminated sites are a threat to human health when left untreated and lead to significant economic costs [1]
For the first time, that the seed microbiome of a pioneer plant growing in its natural environment, and the colonisation behaviour of an important plant growth promoting systemic seed endophyte
This paper describes for the first time the seed core microbiome of Crotalaria pumila, and presents the full characterized potential of its dominant colonizer, Methylobacterium sp
Summary
Metal contaminated sites are a threat to human health when left untreated and lead to significant economic costs [1]. On natural metalliferous soils and mine tailings (waste heaps), metallophyte plants can be found which are tolerant to high concentrations of trace metals. Several mechanisms are at the basis of metal detoxification, including the sequestration of trace metals in the vacuole or apoplast and/or the complexation of metals with metal-binding peptides, such as metallothioneines and phytochelatins [5,6]. In contrast to these metallophytes, most agricultural crops are very sensitive to elevated metal concentrations in soils. It is of crucial importance to develop methods to reclaim heavily disturbed metal contaminated sites, and improve plant growth and metal tolerance
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