Biology in the Dry Seed: Transcriptome Changes Associated with Dry Seed Dormancy and Dormancy Loss in the Arabidopsis GA-Insensitive sleepy1-2 Mutant.

Sven K Nelson,Camille M Steber,Tohru Ariizumi

doi:10.3389/fpls.2017.02158

Abstract

Plant embryos can survive years in a desiccated, quiescent state within seeds. In many species, seeds are dormant and unable to germinate at maturity. They acquire the capacity to germinate through a period of dry storage called after-ripening (AR), a biological process that occurs at 5–15% moisture when most metabolic processes cease. Because stored transcripts are among the first proteins translated upon water uptake, they likely impact germination potential. Transcriptome changes associated with the increased seed dormancy of the GA-insensitive sly1-2 mutant, and with dormancy loss through long sly1-2 after-ripening (19 months) were characterized in dry seeds. The SLY1 gene was needed for proper down-regulation of translation-associated genes in mature dry seeds, and for AR up-regulation of these genes in germinating seeds. Thus, sly1-2 seed dormancy may result partly from failure to properly regulate protein translation, and partly from observed differences in transcription factor mRNA levels. Two positive regulators of seed dormancy, DELLA GAI (GA-INSENSITIVE) and the histone deacetylase HDA6/SIL1 (MODIFIERS OF SILENCING1) were strongly AR-down-regulated. These transcriptional changes appeared to be functionally relevant since loss of GAI function and application of a histone deacetylase inhibitor led to decreased sly1-2 seed dormancy. Thus, after-ripening may increase germination potential over time by reducing dormancy-promoting stored transcript levels. Differences in transcript accumulation with after-ripening correlated to differences in transcript stability, such that stable mRNAs appeared AR-up-regulated, and unstable transcripts AR-down-regulated. Thus, relative transcript levels may change with dry after-ripening partly as a consequence of differences in mRNA turnover.

Highlights

Plant colonization of dry land was made possible by the evolution of seeds as a means of propagation
This paper examines the pattern of transcript accumulation in dry seeds associated with increased seed dormancy and dormancy loss in the GA-insensitive sly1-2 mutant of Arabidopsis
In order to ask specific questions regarding the initial transcriptome state of dormant and non-dormant sly1-2 seeds, an Affymetrix R oligonucleotide-based microarray transcriptome analysis was conducted on dry seeds of: (a) wild-type Landsberg erecta (Ler) (WT) stored for 2 weeks, (b) dormant sly1-2 stored for 2 weeks [sly1-2(D)], (c) after-ripened sly1-2 stored for 19 months [sly1-2(AR)], and d) sly1-2 GID1b-overexpressed stored for 2 weeks (Figure 1C)

Summary

Introduction

Plant colonization of dry land was made possible by the evolution of seeds as a means of propagation. The after-ripening time required for dormancy loss depends on genotype, and can be perturbed through altered function of dormancy-regulating genes (Ariizumi and Steber, 2007; Chiang et al, 2011; Kendall et al, 2011; reviewed in Koornneef and Alonso-Blanco, 2000; reviewed in Nonogaki, 2014) This genetic variation is important in cereal crops where lack of seed dormancy can lead to problems with preharvest sprouting, the germination of grain on the mother plant when cool and rainy conditions occur before harvest (reviewed by Rodríguez et al, 2015). Informed genetic strategies may allow us to increase seed dormancy sufficiently to prevent preharvest sprouting without causing problems with poor germination and emergence when winter crops are planted in the fall with little after-ripening

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