Genome-Wide Association Studies of Seed Performance Traits in Response to Heat Stress in Medicago truncatula Uncover MIEL1 as a Regulator of Seed Germination Plasticity.

Zhijuan Chen,Olivier Leprince,Jerome Verdier,Joseph Ly Vu,Benoit Ly Vu,Julia Buitink

doi:10.3389/fpls.2021.673072

Zhijuan Chen, Olivier Leprince + Show 4 more

Open Access

https://doi.org/10.3389/fpls.2021.673072

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Abstract

Legume seeds are an important source of proteins, minerals, and vitamins for human and animal diets and represent a keystone for food security. With climate change and global warming, the production of grain legumes faces new challenges concerning seed vigor traits that allow the fast and homogenous establishment of the crop in a wide range of environments. These seed performance traits are regulated during seed maturation and are under the strong influence of the maternal environment. In this study, we used 200 natural Medicago truncatula accessions, a model species of legumes grown in optimal conditions and under moderate heat stress (26°C) during seed development and maturation. This moderate stress applied at flowering onwards impacted seed weight and germination capacity. Genome-wide association studies (GWAS) were performed to identify putative loci or genes involved in regulating seed traits and their plasticity in response to heat stress. We identified numerous significant quantitative trait nucleotides and potential candidate genes involved in regulating these traits under heat stress by using post-GWAS analyses combined with transcriptomic data. Out of them, MtMIEL1, a RING-type zinc finger family gene, was shown to be highly associated with germination speed in heat-stressed seeds. In Medicago, we highlighted that MtMIEL1 was transcriptionally regulated in heat-stressed seed production and that its expression profile was associated with germination speed in different Medicago accessions. Finally, a loss-of-function analysis of the Arabidopsis MIEL1 ortholog revealed its role as a regulator of germination plasticity of seeds in response to heat stress.

Highlights

Legume is an economically important crop family, that includes many plant species such as soybean, pea, common bean, and chickpea
To evaluate the impact of heat stress on seed yield and vigor, 200 M. truncatula accessions from the haplotype map (HapMap) collection were grown in triplicate in optimal (20◦C/18◦C) and supraoptimal temperature (i.e., 26◦C/24◦C) conditions by applying constant but moderate heat stress from flowering until pod abscission
Seeds produced in heat stress conditions displayed an overall tendency to germinate faster and more homogeneously than those produced in optimal conditions (Figure 1, phenotypes named T50_C and T80T20_C for optimal and T50_H and T80T20_H for heat stress conditions)

Summary

Introduction

Legume is an economically important crop family, that includes many plant species such as soybean, pea, common bean, and chickpea. In Medicago (Righetti et al, 2015), like many other species (Finch-Savage and Bassel, 2016; Penfield and MacGregor, 2017), seed vigor is drastically affected by environmental conditions during seed development This highly plastic response from the offspring to the environment is considered a bet-hedging strategy to ensure the dissemination of the species. In this respect, one of the most studied germination vigor traits is dormancy (for review, Penfield and MacGregor, 2017). The plastic response of the germination of seeds produced under environmental conditions is dependent on complex GxE interactions of the regulation of physiological dormancy involving zygotic and maternal tissues (Penfield and MacGregor, 2017; Awan et al, 2018; Geshnizjani et al, 2019; Chen et al, 2020; Renzi et al, 2020), and the dynamic balance between ABA and GA is poorly understood and likely to be species-dependent (Penfield and MacGregor, 2017; Chen et al, 2020)

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