Involvement of ethylene biosynthesis and perception during germination of dormant Avena fatua L. caryopses induced by KAR1 or GA3

Abstract

Main conclusion Germination of primary dormant wild oat caused by KAR 1 or GA 3 is associated with ACC accumulation and increased ethylene production shortly before radicle protrusion as a result of the non-transcriptional and transcriptional activation of ACS and ACO enzymes, respectively. Response to both compounds involves the modulation of ethylene sensitivity through ethylene receptor genes. Harvested Avena fatua caryopses are primary dormant and, therefore, germinated poorly at 20 °C. Karrikin 1 (KAR 1), which action probably requires endogenous gibberellins (GAs), and gibberellin A 3 (GA 3) was found to induce dormant caryopses to germinate. The stimulatory effects were accompanied by the activation of the ethylene biosynthesis pathway and depended on undisturbed ethylene perception. KAR 1 and GA 3 promoted 1-aminocyclopropane-1-carboxylic acid (ACC) accumulation during coleorhizae emergence and ethylene production shortly prior to the radicle protrusion, which resulted from the enhanced activity of two ethylene biosynthesis enzymes, ACC synthase (ACS) and ACC oxidase (ACO). The inhibitor of ACS adversely affected beneficial impacts of both KAR 1 and GA 3 on A. fatua caryopses germination, while the inhibitor of ACO more efficiently impeded the GA 3 effect. The inhibitors of ethylene action markedly lowered germination in response to KAR 1 and GA 3. Gene expression studies preceded by the identification of several genes related to ethylene biosynthesis (AfACS6, AfACO1, and AfACO5) and perception (AfERS1b, AfERS1c, AfERS2, AfETR2, AfETR3, and AfETR4) provided further evidence for the engagement of ethylene in KAR 1 and GA 3 induced germination of A. fatua caryopses. Both AfACO1 and AfACO5 were upregulated, whereas AfACS6 remained unaffected by the treatment. This suggests the existence of different regulatory mechanisms of enzymatic activity, transcriptional for ACO and non-transcriptional for ACS. During imbibition in water, AfERS1b was stronger expressed than other receptor genes. In the presence of KAR 1 or GA 3 , the expression of AfETR3 was substantially induced. Differential expression of ethylene receptor genes implies the modulation of caryopses sensitivity adjusted to ethylene availability and suggests the functional diversification of individual receptors.

Exogenous gibberellin and cytokinin in a novel system for in vitro germination and development of African iris (Dietes bicolor)

“…The regulation of the germination process involves the hormonal balance between abscisic acid (ABA) and GA. While ABA promotes the establishment and maintenance of seed dormancy, GA acts in an antagonistic way, stimulating germination (Phengphachanh et al, 2012;Ruduoe et al, 2019). In fact, in the present study the highest germination rate was observed in the medium supplemented with the highest GA concentration.…”

Coleorhiza‐enforced seed dormancy: a novel mechanism to control germination in grasses

“…1d). Fresh mature A. fatua diaspores exhibited physiological dormancy, which is controlled by hormones: ABA is involved in maintaining (Jones et al ., 2000) while GA and ethylene are involved in releasing this dormancy (Ruduś et al ., 2019). Treatment of dormant (D) A. fatua diaspores with GA or 4 months of dry storage (‘after‐ripening’) caused dormancy release (Figs 1e,f, S1) and upon imbibition, emergence of the coleorhiza was the first visible step during the germination process (Fig.…”

“…The coleorhiza is widespread beyond the grasses in other monocot species and in cycads but is absent in eudicots. Upon dormancy release, GA and ethylene induce the expression of CWRP genes including expansins, cellulases, mannanases and XTHs in the micropylar endosperm of eudicot seeds (Chen & Bradford, 2000; Toorop et al ., 2000; Chen et al ., 2002; Finch‐Savage & Leubner‐Metzger, 2006; Linkies et al ., 2009; Lee et al ., 2012; Martinez‐Andujar et al ., 2012; Graeber et al ., 2014) and the coleorhiza of Poaceae caryopses (Millar et al ., 2006; Barrero et al ., 2009; Gonzalez‐Calle et al ., 2015; Ruduś et al ., 2019) including A. fatua (this work). Interestingly, expansins are also expressed in the overlaying tissues during lateral root formation and the importance of the mechanical properties and of tissue interactions was proposed (Lucas et al ., 2013; Ramakrishna et al ., 2019).…”

SMAX1/SMXL2 regulate root and root hair development downstream of KAI2-mediated signalling in Arabidopsis

“…In fire-following species, karrikins are used as germination cues, indicating the removal of competing plants. However, karrikins promote germination in a range of flowering plant species, which do not germinate after fire [24–26] and KAI2 is required for a number of developmental traits in Arabidopsis not related to germination as well as for arbuscular mycorrhiza symbiosis in rice [19, 27–30]. Because of these roles of KAI2, karrikins are thought to mimic the action of a yet unknown endogenous plant signalling molecule, which is currently denoted KAI2-ligand (KL) [31–33].…”