Seed Dormancy Involves a Transcriptional Program That Supports Early Plastid Functionality during Imbibition

Abstract

Red rice fully dormant seeds do not germinate even under favorable germination conditions. In several species, including rice, seed dormancy can be removed by dry-afterripening (warm storage); thus, dormant and non-dormant seeds can be compared for the same genotype. A weedy (red) rice genotype with strong dormancy was used for mRNA expression profiling, by RNA-Seq, of dormant and non-dormant dehulled caryopses (here addressed as seeds) at two temperatures (30 °C and 10 °C) and two durations of incubation in water (8 h and 8 days). Aim of the study was to highlight the differences in the transcriptome of dormant and non-dormant imbibed seeds. Transcript data suggested important differences between these seeds (at least, as inferred by expression-based metabolism reconstruction): dry-afterripening seems to impose a respiratory impairment onto non-dormant seeds, thus glycolysis is deduced to be preferentially directed to alcoholic fermentation in non-dormant seeds but to alanine production in dormant ones; phosphoenolpyruvate carboxykinase, pyruvate phosphate dikinase and alanine aminotransferase pathways appear to have an important gluconeogenetic role associated with the restoration of plastid functions in the dormant seed following imbibition; correspondingly, co-expression analysis pointed out a commitment to guarantee plastid functionality in dormant seeds. At 8 h of imbibition, as inferred by gene expression, dormant seeds appear to preferentially use carbon and nitrogen resources for biosynthetic processes in the plastid, including starch and proanthocyanidins accumulation. Chromatin modification appears to be a possible mechanism involved in the transition from dormancy to germination. Non-dormant seeds show higher expression of genes related to cell wall modification, suggesting they prepare for acrospire/radicle elongation.

Ascorbic acid and prunasin, two candidate biomarkers for endodormancy release in almond flower buds identified by a nontargeted metabolomic study

“…3B). It is known that during endodormancy release in red-rice seeds, the glycolysis and energy obtained increase 42 ; these findings agree with the increase in the compounds from D-sorbitol metabolism that we could observe in the extra-early Desmayo Largueta cultivar, suggesting the role this metabolite plays in early endodormancy release.…”

Pseudophoenix ekmanii (Arecaceae) seeds at suboptimal temperature show reduced imbibition rates and enhanced expression of genes related to germination inhibition

“…For example, two loci encoding for alanine aminotransferase were up‐regulated at 20 °C (LOC105041987 and LOC105058582). Dormant imbibed seeds of red rice also showed overexpression of two alanine aminotransferases in comparison to non‐dormant seeds (Gianinetti et al 2018), and in barley, different alleles of an alanine aminotransferase that is specifically expressed in the embryo appear to control seed dormancy depth (Sato et al 2016).…”

“…Similarly, the GO categories ‘Lipid biosynthetic process’ and ‘Regulation of starch biosynthetic process’ seem to point to an accumulation of storage molecules that is generally associated with seed maturation rather than germination (Lee et al 2015; Chahtane et al 2017). Indeed, Gianinetti et al (2018) inferred that in dormant, imbibed red rice seeds, sugars are partially accumulated as starch in the proplastids. Finally, the presence of methylglyoxal catabolic processes indicates potentially high levels of this molecule in the embryos.…”

A response of the imbibed dormant red rice caryopsis to biotic challenges involves extracellular pH increase to elicit superoxide production

“…Besides, mechanical resistance of the caryopsis coats could be enforced, as PAs polymerize to large, poorly soluble phlobaphenes (Finocchiaro et al , 2007). PAs release therefore appears to represent a pre-emptive strategy that dormant seeds adopt to protect themselves from intrusive assaults by other organisms (Gianinetti et al , 2018). Remarkably, pronase-induced defence response favours polymerization of colourless PAs to red phlobaphenes, as indicated by the colour change of the caryopsis (Fig.…”