Transcriptional Differences in Peanut (Arachis hypogaea L.) Seeds at the Freshly Harvested, After-ripening and Newly Germinated Seed Stages: Insights into the Regulatory Networks of Seed Dormancy Release and Germination.

Pingli Xu,Guangxia Chen,Lei Shan,Weipei Cui,Pengxiang Li,Jieqiong Zhu,Shubo Wan,Chang-Le Ma,Guiying Tang,Zhanji Liu

doi:10.1371/journal.pone.0219413

Abstract

Seed dormancy and germination are the two important traits related to plant survival, reproduction and crop yield. To understand the regulatory mechanisms of these traits, it is crucial to clarify which genes or pathways participate in the regulation of these processes. However, little information is available on seed dormancy and germination in peanut. In this study, seeds of the variety Luhua No.14, which undergoes nondeep dormancy, were selected, and their transcriptional changes at three different developmental stages, the freshly harvested seed (FS), the after-ripening seed (DS) and the newly germinated seed (GS) stages, were investigated by comparative transcriptomic analysis. The results showed that genes with increased transcription in the DS vs FS comparison were overrepresented for oxidative phosphorylation, the glycolysis pathway and the tricarboxylic acid (TCA) cycle, suggesting that after a period of dry storage, the intermediates stored in the dry seeds were rapidly mobilized by glycolysis, the TCA cycle, the glyoxylate cycle, etc.; the electron transport chain accompanied by respiration was reactivated to provide ATP for the mobilization of other reserves and for seed germination. In the GS vs DS pairwise comparison, dozens of the upregulated genes were related to plant hormone biosynthesis and signal transduction, including the majority of components involved in the auxin signal pathway, brassinosteroid biosynthesis and signal transduction as well as some GA and ABA signal transduction genes. During seed germination, the expression of some EXPANSIN and XYLOGLUCAN ENDOTRANSGLYCOSYLASE genes was also significantly enhanced. To investigate the effects of different hormones during seed germination, the contents and differential distribution of ABA, GAs, BRs and IAA in the cotyledons, hypocotyls and radicles, and plumules of three seed sections at different developmental stages were also investigated. Combined with previous data in other species, it was suggested that the coordination of multiple hormone signal transduction nets plays a key role in radicle protrusion and seed germination.

Highlights

Seed dormancy and germination are the two important traits in the plant life cycle involved in species survival and offspring proliferation
After a period of dry storage, the majority of dried seeds started to germinate at two DAI, and their germination rates significantly increased at four DAI and reached 100%, 97.2%, and 97.2% at germination six DAI
The duration of the AR process varies greatly among species: some last for several days, and others last for several months or more [10, 15, 25].The physiological status of dry seeds seems to be quiescent; abundant changes in gene expression have been found in dry seeds compared to dormant seeds, which are triggered by AR [42,43,44]

Summary

Introduction

Seed dormancy and germination are the two important traits in the plant life cycle involved in species survival and offspring proliferation. Different plant species present various classes of dormancy to regulate the timing of seed germination and to help seedlings emerge under favorable conditions. During the subsequent dry period of seeds (so-called after-ripening, AR), primary dormancy slowly decreases. When the dormancy level gradually decreases, seeds can rapidly exit dormancy and proceed to germination during imbibition under favorable conditions [1]. A recent study in Arabidopsis suggested that seed AR is a specific developmental pathway that is independent of germination potential and does not rely on ABA regulation [2]. The metabolic switches between different developmental periods of seeds are relevant to the distinct expression profiles of genes involved in several metabolic pathways [6]

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Conclusion