Mitogen-Activated Protein Kinase Kinase 3 Regulates Seed Dormancy in Barley

Abstract

Seed dormancy has fundamental importance in plant survival and crop production; however, the mechanisms regulating dormancy remain unclear [1-3]. Seed dormancy levels generally decrease during domestication to ensure that crops successfully germinate in the field. However, reduction of seed dormancy can cause devastating losses in cereals like wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) due to pre-harvest sprouting, the germination of mature seed (grain) on the mother plant when rain occurs before harvest. Understanding the mechanisms of dormancy can facilitate breeding of crop varieties with the appropriate levels of seed dormancy [4-8]. Barley is a model crop [9, 10] and has two major seed dormancy quantitative trait loci (QTLs), SD1 and SD2, on chromosome 5H [11-19]. We detected a QTL designated Qsd2-AK at SD2 as the single major determinant explaining the difference in seed dormancy between the dormant cultivar "Azumamugi" (Az) and the non-dormant cultivar "Kanto Nakate Gold" (KNG). Using map-based cloning, we identified the causal gene for Qsd2-AK as Mitogen-activated Protein Kinase Kinase 3 (MKK3). The dormant Az allele of MKK3 is recessive; the N260T substitution in this allele decreases MKK3 kinase activity and appears to be causal for Qsd2-AK. The N260T substitution occurred in the immediate ancestor allele of the dormant allele, and the established dormant allele became prevalent in barley cultivars grown in East Asia, where the rainy season and harvest season often overlap. Our findings show fine-tuning of seed dormancy during domestication and provide key information for improving pre-harvest sprouting tolerance in barley and wheat.

Seed Biology Updates – Highlights and New Discoveries in Seed Dormancy and Germination Research

“…There were more findings relevant to hormonal signaling (Jiang et al, 2016), seed structures (Graeber et al, 2014; De Giorgi et al, 2015), crop seed dormancy (Nakamura et al, 2016; Sato et al, 2016; Torada et al, 2016) and many others, which were not integrated into this review due to the limited space and the scope of this article. Different dots and lines provided by other findings will probably be connected to each other by more discoveries in the near future.…”

Convergence of Multiple MAP3Ks on MKK3 Identifies a Set of Novel Stress MAPK Modules

“…A very recent study similarly reported that Nicotiana benthamiana plants over-expressing the cotton ( Gossypium hirsutum ) GhMKK3 were more resistant to drought and closed more efficiently their stomata in response to ABA (Wang et al, 2016). Additionally, by QTL mapping for seed dormancy, two recessive mutations in MKK3 orthologs have been identified in both wheat and barley (Nakamura et al, 2016; Torada et al, 2016). In plants, dormancy is under control of seed hormonal content during maturation and desiccation, with one of the main hormones being ABA (Shu et al, 2016).…”

“…In plants, dormancy is under control of seed hormonal content during maturation and desiccation, with one of the main hormones being ABA (Shu et al, 2016). In the case of the barley mutant cultivar “Azumamugi,” the recessive mutation decreases MKK3 activity and thereby increases seed dormancy, suggesting that the activation of the MKK3 module releases seed dormancy (Nakamura et al, 2016). …”

Insights into Seasonal Dormancy of Perennial Herbaceous Forages

“…reduced seed dormancy causes pre-harvest sprouting resulting in significant yield loss [125]. Barley has two major quantitative traits (QTL) for seed dormancy, SD1 and SD2, on chromosome 5H [125].…”

“…Barley has two major quantitative traits (QTL) for seed dormancy, SD1 and SD2, on chromosome 5H [125]. Nakamura et al also reported that mitogen-activated protein kinase cascade regulates seed dormancy in barley [125].…”