Common oat (Avena sativa) is an important cereal crop serving as a valuable source of forage and human food. Although reference genomes of many important crops have been generated, such work in oat has lagged behind, primarily owing to its large, repeat-rich polyploid genome. Here, using Oxford Nanopore ultralong sequencing and Hi-C technologies, we have generated a reference-quality genome assembly of hulless common oat, comprising 21 pseudomolecules with a total length of 10.76 Gb and contig N50 of 75.27 Mb. We also produced genome assemblies for diploid and tetraploid Avena ancestors, which enabled the identification of oat subgenomes and provided insights into oat chromosomal evolution. The origin of hexaploid oat is inferred from whole-genome sequencing, chloroplast genomes and transcriptome assemblies of different Avena species. These findings and the high-quality reference genomes presented here will facilitate the full use of crop genetic resources to accelerate oat improvement.

Naked oat (Avena nuda L.) was originated from China, where there soil nitrogen (N) is low availability. The responses of chlorophyll (Chl) fluorescence parameters and leaf gas exchange to N application were analysed in this study. After the N application rate ranged from 60 to 120 kg hm-2 , variable fluorescence (Fv), maximal fluorescence (Fm), maximal photochemical efficiency (Fv/Fm), quantum yield (ΦPSII) of the photosynthetic system II (PSII), electron transport rate (ETR) and photochemical quenching coefficient (qP) increased with N application level, however, non-photochemical quenching coefficient (qN) decreased. Moreover, there was no difference in initial fluorescence (Fo) with further more N enhancement. Maximum net photosynthetic rate (Pmax), apparent dark respiration rate (Rd) and light saturation point (LSP) were improved with 40-56 kg N ha-1 as basal fertilizer and 24-40 kg N ha-1 as top dressing fertilizer applied at jointing stage. Initial quantum yield (α) was decreased with 24 kg N ha-1 as basal fertilizer and 56 kg N ha-1 as top dressing fertilizer. Flag-leaf net photosynthetic rate (Pn) was significantly enhanced at the jointing and heading stages with 40-56 kg N ha-1 as basal fertilizer; in addition, increased at grain filling stage of naked oat with 40-56 kg N ha-1 as top dressing fertilizer. 90 kg N ha-1 (50-70% as basal fertilizer and 30-50% as top dressing fertilizer) application is recommended to alleviate photodamage of photosystem and improve the photosynthetic rate in naked oat.

Common oat (Avena sativa) is one of the most important cereal crops serving as a valuable source of forage and human food. While reference genomes of many important crops have been generated, such work in oat has lagged behind, primarily owing to its large, repeat-rich, polyploid genome. By using Oxford Nanopore ultralong sequencing and Hi-C technologies, we have generated the first reference-quality genome assembly of hulless common oat with a contig N50 of 93 Mb. We also assembled the genomes of diploid and tetraploid Avena ancestors, which enabled us to identify oat subgenome, large-scale structural rearrangements, and preferential gene loss in the C subgenome after hexaploidization. Phylogenomic analyses of cereal crops indicated that the oat lineage descended before wheat, offering oat as a unique window into the early evolution of polyploid plants. The origin and evolution of hexaploid oat is deduced from whole-genome sequencing, plastid genome and transcriptomes assemblies of numerous Avena species. The high-quality reference genomes of Avena species with different ploidies and the studies of their polyploidization history will facilitate the full use of crop gene resources and provide a reference for the molecular mechanisms underlying the polyploidization of higher plants, helping us to overcome food security challenges.

This study investigated the effect of fermentation on the physicochemical properties of b-glucans in oat sourdough. Sourdoughs were produced from oat using homo-fermentative lactic acid bacteria, Lactobacillus plantarum 22134. The contents of total b-glucan and soluble b-glucan, the molecular weight (MW) of b-glucan and the viscosity of the extracted b-glucans were determined at 0, 4, 8, 10 and 12 h of fermentation. The total b-glucan content decreased from 4.89% to 4.23% after 12 h of fermentation. The soluble b-glucan concentration increased from 1.89% to 2.18% and then decreased to 1.97% after 8 h of fermentation. The content of b-glucans with MW > 10 5 decreased from 0 to 4 h of fermentation, followed by an increase and then a decrease after 8 h. The oat sourdough fermented for 8 h had high viscosity, which could be more beneficial for health and bread texture quality, especially for gluten-free breads.

Oat seed with dormancy characteristics, which can germinate after one season or one year, are used to build and maintain vegetation to protect soils from been damaged by desertification in Northern China. The aim of this study was to estimate the effects of endogenous and exogenous GA3 and ABA on oat seed (var. Baiyan 7) germination. The results showed that seeds without peel hull had lower endogenous ABA content and the ratio of ABA/GA3 than seeds with peel hull. The best GA3 treatment duration for milky ripe, wax ripe, full ripe seeds were 60 min or 120 min, 60 min and 30 min, respectively. Seed germination rate, germination potential and germination index increased before they declined with the increasing of GA3 concentrations. The best GA3 concentration treatment was 100 mg/l, while the turning point was 200 mg/l. The dormancy rate of low temperature storage seeds were higher than those of room temperature storage seeds at each storage time, and both decreased with the increase of the storage time. For the seeds which were new or stored for 1-2 months, the germination rates were enhanced significantly by exogenous GA3. For the seeds that had been stored for over three months, GA3 treatment had no effect on germination rate. Germination rate decreased with the increase of ABA concentrations. The most inhibitive effect, which leaded to a seed germination reduction by 37.7% and 4.0%, appeared, when the concentration of ABA was 500 mg/L and 1000 mg/l, respectively. GA3 could abate the effect which ABA inhibited seed germination.