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Abstract
Karrikins (KAR) are a class of signal compounds, discovered in wildfire smoke, which affect seed germination. Currently, numerous studies have focused on the model plant Arabidopsis in the KAR research field, rather than on crops. Thus the regulatory mechanisms underlying KAR regulation of crop seed germination are largely unknown. Here, we report that KAR delayed soybean seed germination through enhancing abscisic acid (ABA) biosynthesis, while impairing gibberellin (GA) biogenesis. Interestingly, KAR only retarded soybean seed germination under shaded conditions, rather than under dark and white light conditions, which differs from in Arabidopsis. Phytohormone quantification showed that KAR enhanced ABA biogenesis while impairing GA biosynthesis during the seed imbibition process, and subsequently, the ratio of active GA4 to ABA was significantly reduced. Further qRT-PCR analysis showed that the transcription pattern of genes involved in ABA and GA metabolic pathways are consistent with the hormonal measurements. Finally, fluridone, an ABA biogenesis inhibitor, remarkably rescued the delayed-germination phenotype of KAR-treatment; and paclobutrazol, a GA biosynthesis inhibitor, inhibited soybean seed germination. Taken together, these evidences suggest that KAR inhibit soybean seed germination by mediating the ratio between GA and ABA biogenesis.
Highlights
Soybean (Glycine max L.), a legume species native to East Asia, is widely grown as the primary oilseed crop in the world including in the United States, Brazil, Argentina, India and China[1,2]
The results showed that GmSTH7 and GmKUF1 were significantly up-regulated after KAR treatment in soybean seeds (Fig. 1)
The detailed physiological analysis of germination, phytohormone measurements and gene expression analysis demonstrated that KAR negatively regulated soybean seed germination and post-germination growth, in a manner distinctly different from that in Arabidopsis
Summary
Soybean (Glycine max L.), a legume species native to East Asia, is widely grown as the primary oilseed crop in the world including in the United States, Brazil, Argentina, India and China[1,2]. Soybean seeds contain high oil and protein contents, and possess a rigid and impermeable seed coat or hull[4,5] These limiting factors result in poor germination and emergence in the field, which significantly decreases soybean yield, especially under stress conditions[6]. A recent study demonstrated that cold plasma treatment significantly promotes soybean seed germination and thereafter seedling establishment and growth processes[4], the mechanisms underlying this positive effect are elusive. The promotion effect of H2O2 has been documented in diverse species, including maize[13], wheat[14] and Arabidopsis[15,16], suggesting conserved roles of reactive oxygen species in seed germination in dicots and monocots. Numerous studies on Arabidopsis demonstrated that ABA and GA play key roles in regulating seed germination, and antagonistically regulate this process[17,18]. Quantification of ABA and GA and analyses of the transcription of key genes involved in hormonal metabolism pathways are validated approaches in the seed germination research field
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