Impacts of drought and elevated temperature on the seeds of malting barley.

High seed quality is key to agricultural production, which is increasingly affected by climate change. We studied the effects of drought and elevated temperature during seed production on key seed quality traits of two genotypes of malting barley (Hordeum sativum L.). Plants of a "Hana-type" landrace (B1) were taller, flowered earlier and produced heavier, larger and more vigorous seeds that resisted ageing longer compared to a semi-dwarf breeding line (B2). Accordingly, a NAC domain-containing transcription factor (TF) associated with rapid response to environmental stimuli, and the TF ABI5, a key regulator of seed dormancy and vigour, were more abundant in B1 seeds. Drought significantly reduced seed yield in both genotypes, and elevated temperature reduced seed size. Genotype B2 showed partial thermodormancy that was alleviated by drought and elevated temperature. Metabolite profiling revealed clear differences between the embryos of B1 and B2. Drought, but not elevated temperature, affected the metabolism of amino acids, organic acids, osmolytes and nitrogen assimilation, in the seeds of both genotypes. Our study may support future breeding efforts to produce new lodging and drought resistant malting barleys without trade-offs that can occur in semi-dwarf varieties such as lower stress resistance and higher dormancy.

Corrigendum: Genotypic Variation of Nitrogen Use Efficiency and Amino Acid Metabolism in Barley.

[This corrects the article DOI: 10.3389/fpls.2021.807798.].

Genotypic Variation of Nitrogen Use Efficiency and Amino Acid Metabolism in Barley.

Owing to the large genetic diversity of barley and its resilience under harsh environments, this crop is of great value for agroecological transition and the need for reduction of nitrogen (N) fertilizers inputs. In the present work, we investigated the diversity of a North African barley genotype collection in terms of growth under limiting N (LN) or ample N (HN) supply and in terms of physiological traits including amino acid content in young seedlings. We identified a Moroccan variety, Laanaceur, accumulating five times more lysine in its leaves than the others under both N nutritional regimes. Physiological characterization of the barley collection showed the genetic diversity of barley adaptation strategies to LN and highlighted a genotype x environment interaction. In all genotypes, N limitation resulted in global biomass reduction, an increase in C concentration, and a higher resource allocation to the roots, indicating that this organ undergoes important adaptive metabolic activity. The most important diversity concerned leaf nitrogen use efficiency (LNUE), root nitrogen use efficiency (RNUE), root nitrogen uptake efficiency (RNUpE), and leaf nitrogen uptake efficiency (LNUpE). Using LNUE as a target trait reflecting barley capacity to deal with N limitation, this trait was positively correlated with plant nitrogen uptake efficiency (PNUpE) and RNUpE. Based on the LNUE trait, we determined three classes showing high, moderate, or low tolerance to N limitation. The transcriptomic approach showed that signaling, ionic transport, immunity, and stress response were the major functions affected by N supply. A candidate gene encoding the HvNRT2.10 transporter was commonly up-regulated under LN in the three barley genotypes investigated. Genes encoding key enzymes required for lysine biosynthesis in plants, dihydrodipicolinate synthase (DHPS) and the catabolic enzyme, the bifunctional Lys-ketoglutarate reductase/saccharopine dehydrogenase are up-regulated in Laanaceur and likely account for a hyperaccumulation of lysine in this genotype. Our work provides key physiological markers of North African barley response to low N availability in the early developmental stages.

Multi-omics Analysis Reveals Sequential Roles for ABA during Seed Maturation.

Abscisic acid (ABA) is an important hormone for seed development and germination whose physiological action is modulated by its endogenous levels. Cleavage of carotenoid precursors by 9-cis epoxycarotenoid dioxygenase (NCED) and inactivation of ABA by ABA 8'-hydroxylase (CYP707A) are key regulatory metabolic steps. In Arabidopsis (Arabidopsis thaliana), both enzymes are encoded by multigene families, having distinctive expression patterns. To evaluate the genome-wide impact of ABA deficiency in developing seeds at the maturation stage when dormancy is induced, we used a nced2569 quadruple mutant in which ABA deficiency is mostly restricted to seeds, thus limiting the impact of maternal defects on seed physiology. ABA content was very low in nced2569 seeds, similar to the severe mutant aba2; unexpectedly, ABA Glc ester was detected in aba2 seeds, suggesting the existence of an alternative metabolic route. Hormone content in nced2569 seeds compared with nced259 and wild type strongly suggested that specific expression of NCED6 in the endosperm is mainly responsible for ABA production. In accordance, transcriptome analyses revealed broad similarities in gene expression between nced2569 and either wild-type or nced259 developing seeds. Gene ontology enrichments revealed a large spectrum of ABA activation targets involved in reserve storage and desiccation tolerance, and repression of photosynthesis and cell cycle. Proteome and metabolome profiles in dry nced2569 seeds, compared with wild-type and cyp707a1a2 seeds, also highlighted an inhibitory role of ABA on remobilization of reserves, reactive oxygen species production, and protein oxidation. Down-regulation of these oxidative processes by ABA may have an essential role in dormancy control.

Novel loci and a role for nitric oxide for seed dormancy and preharvest sprouting in barley.

Barley is used for food and feed, and brewing. Nondormant seeds are required for malting, but the lack of dormancy can lead to preharvest sprouting (PHS), which is also undesired. Here, we report several new loci that modulate barley seed dormancy and PHS. Using genome-wide association mapping of 184 spring barley genotypes, we identified four new, highly significant associations on chromosomes 1H, 3H, and 5H previously not associated with barley seed dormancy or PHS. A total of 71 responsible genes were found mostly related to flowering time and hormone signalling. A homolog of the well-known Arabidopsis Delay of Germination 1 (DOG1) gene was annotated on the barley chromosome 3H. Unexpectedly, DOG1 appears to play only a minor role in barley seed dormancy. However, the gibberellin oxidase gene HvGA20ox1 contributed to dormancy alleviation, and another seven important loci changed significantly during after-ripening. Furthermore, nitric oxide release correlated negatively with dormancy and shared 27 associations. Origin and growth environment affected seed dormancy and PHS more than did agronomic traits. Days to anthesis and maturity were shorter when seeds were produced under drier conditions, seeds were less dormant, and PHS increased, with a heritability of 0.57-0.80. The results are expected to be useful for crop improvement.

Role of protein farnesylation events in the ABA-mediated regulation of the Pinoresinol-Lariciresinol Reductase 1 (LuPLR1) gene expression and lignan biosynthesis in flax (Linum usitatissimum L.).

A Linum usitatissimum LuERA1 gene encoding a putative ortholog of the ERA1 (Enhanced Response to ABA 1) gene of Arabidopsis thaliana (encoding the beta subunit of a farnesyltransferase) was analyzed in silico and for its expression in flax. The gene and the protein sequences are highly similar to other sequences already characterized in plants and all the features of a farnesyltransferase were detected. Molecular modeling of LuERA1 protein confirmed its farnesyltransferase nature. LuERA1 is expressed in the vegetative organs and also in the outer seedcoat of the flaxseed, where it could modulate the previously observed regulation operated by ABA on lignan synthesis. This effect could be mediated by the regulation of the transcription of a key gene for lignan synthesis in flax, the LuPLR1 gene, encoding a pinoresinol lariciresinol reductase. The positive effect of manumycin A, a specific inhibitor of farnesyltransferase, on lignan biosynthesis in flax cell suspension systems supports the hypothesis of the involvement of such an enzyme in the negative regulation of ABA action. In Arabidopsis, ERA1 is able to negatively regulate the ABA effects and the mutant era1 has an enhanced sensitivity to ABA. When expressed in an Arabidopsis cell suspension (heterologous system) LuERA1 is able to reverse the effect of the era1 mutation. RNAi experiments in flax targeting the farnesyltransferase ß-subunit encoded by the LuERA1 gene led to an increase LuPLR1 expression level associated with an increased content of lignan in transgenic calli. Altogether these results strongly suggest a role of the product of this LuERA1 gene in the ABA-mediated upregulation of lignan biosynthesis in flax cells through the activation of LuPLR1 promoter. This ABA signaling pathway involving ERA1 probably acts through the ABRE box found in the promoter sequence of LuPLR1, a key gene for lignan synthesis in flax, as demonstrated by LuPLR1 gene promoter-reporter experiments in flax cells using wild type and mutated promoter sequences.