Expression of Seed Dormancy in Grain Sorghum Lines with Contrasting Pre-Harvest Sprouting Behavior Involves Differential Regulation of Gibberellin Metabolism Genes

Abstract

Grain sorghum [Sorghum bicolor (L) moench] exhibits intraspecific variability for the rate of dormancy release and pre-harvest sprouting behavior. Two inbred lines with contrasting sprouting response were compared: IS9530 (resistant) and RedlandB2 (susceptible). Precocious dormancy release in RedlandB2 is related to an early loss of embryo sensitivity to ABA and higher levels of gibberellins in imbibed grains as compared with IS9530. With the aim of identifying potential regulatory sites for gibberellin metabolism involved in the expression of dormancy in immature grains of both lines, we carried out a time course analysis of transcript levels of putative gibberellin metabolism genes and hormone content (GA(1), GA(4), GA(8) and GA(34)). A lower embryonic GA(4) level in dormant IS9530 was related to a sharp and transient induction of two SbGA2-oxidase (inactivation) genes. In contrast, these genes were not induced in less dormant RedlandB2, while expression of two SbGA20-oxidase (synthesis) genes increased together with active GA(4) levels before radicle protrusion. Embryonic levels of GA(4) and its catabolite GA(34) correlated negatively. Thus, in addition to the process of gibberellin synthesis, inactivation is also important in regulating GA(4) levels in immature grains. A negative regulation by gibberellins was observed for SbGA20ox2, SbGA2ox1 and SbGA2ox3 and also for SbGID1 encoding a gibberellin receptor. We propose that the coordinated regulation at the transcriptional level of several gibberellin metabolism genes identified in this work affects the balance between gibberellin synthesis and inactivation processes, controlling active GA(4) levels during the expression of dormancy in maturing sorghum grains.

Spatiotemporal Seed Development Analysis Provides Insight into Primary Dormancy Induction and Evolution of theLepidium DELAY OF GERMINATION1Genes

“…In contrast to Arabidopsis, premature seed germination prior to dormancy induction does not require any hormonal addition in L. papillosum (this work), as is also known from Brassica spp. (Fernandez, 1997;Ren and Bewley, 1999) or cereal grains (Rodríguez et al, 2012). However, L. papillosum premature seeds need approximately four times longer to complete germination as compared with mature seeds in which dormancy has been broken (compare Fig.…”

Map-Based Cloning of qSD1-2 Identified a Gibberellin Synthesis Gene Regulating the Development of Endosperm-Imposed Dormancy in Rice

“…Reasons may include that these mutants usually have detrimental effects on gametophyte development or seed setting, some may not express in developing seeds, and research was focused on postgermination events (Kaneko et al, 2003). Natural mutants used to develop semidwarf varieties in the barley (Hordeum vulgare), sorghum (Sorghum bicolor), and wheat crops usually have a mild negative effect on plant development, and some of them are GA sensitive (Gale and Marshall, 1975;Franckowiak and Pecio, 1992;Rodríguez et al, 2012). Some seed dormancy QTLs in barley and wheat have been associated with GA metabolism genes by comparative genomics research using rice as the reference (Li et al, 2004;Cabral et al, 2014).…”

Seed dormancy QTL identification across a Sorghum bicolor segregating population

“…Other features, such as the panicle architecture, glumes or glumellae presence and seed tannin content, which could actually affect the relationship between dormancy and PHS susceptibility, have been shown not to be involved in IS9530/RedlandB2 PHS behaviour (Steinbach et al 1995). Premature release from dormancy in RedlandB2 grains has been ascribed to a reduced sensitivity of their embryos to the germination inhibitory action of abscisic acid (ABA) and an abnormal accumulation of active gibberellins (GAs) (Steinbach et al 1995(Steinbach et al , 1997Rodríguez et al 2009Rodríguez et al , 2012. Both processes (faulty ABA sensitivity and GA inactivation) have been found to be differentially regulated in this line at the transcriptional level of genes involved in ABA signalling and GA catabolism (Rodríguez et al 2009(Rodríguez et al , 2012.…”

“…Premature release from dormancy in RedlandB2 grains has been ascribed to a reduced sensitivity of their embryos to the germination inhibitory action of abscisic acid (ABA) and an abnormal accumulation of active gibberellins (GAs) (Steinbach et al 1995(Steinbach et al , 1997Rodríguez et al 2009Rodríguez et al , 2012. Both processes (faulty ABA sensitivity and GA inactivation) have been found to be differentially regulated in this line at the transcriptional level of genes involved in ABA signalling and GA catabolism (Rodríguez et al 2009(Rodríguez et al , 2012. QTL searches for PHS resistance in immature sorghum grains were attempted previously by Lijavetzky et al (2000) using a RedlandB2 x IS9530 segregating population.…”