Wheat yellow mosaic virus (WYMV) is a pathogen transmitted into its host’s roots by the soil-borne vector Polymyxa graminis . Ym1 and Ym2 genes protect the host from the significant yield losses caused by the virus, but the mechanistic basis of these resistance genes remains poorly understood. Here, it has been shown that Ym1 and Ym2 act within the root either by hindering the initial movement of WYMV from the vector into the root and/or by suppressing viral multiplication. A mechanical inoculation experiment on the leaf revealed that the presence of Ym1 reduced viral infection incidence, rather than viral titer, while that of Ym2 was ineffective in the leaf. To understand the basis of the root specificity of the Ym2 product, the gene was isolated from bread wheat using a positional cloning approach. The candidate gene encodes a CC-NBS-LRR protein and it correlated allelic variation with respect to its sequence with the host’s disease response. Ym2 (B37500) and its paralog (B35800) are found in the near-relatives, respectively, Aegilops sharonensi s and Aegilops speltoides (a close relative of the donor of bread wheat’s B genome), while both sequences, in a concatenated state, are present in several accessions of the latter species . Structural diversity in Ym2 has been generated via translocation and recombination between the two genes and enhanced by the formation of a chimeric gene resulting from an intralocus recombination event. The analysis has revealed how the Ym2 region has evolved during the polyploidization events leading to the creation of cultivated wheat.

Sucrose nonfermenting 2 (Snf2) family proteins, as the catalytic core of ATP-dependent chromatin remodeling complexes, play important roles in nuclear processes as diverse as DNA replication, transcriptional regulation, and DNA repair and recombination. The Snf2 gene family has been characterized in several plant species; some of its members regulate flower development in Arabidopsis. However, little is known about the members of the family in barley (Hordeum vulgare). Here, 38 Snf2 genes unevenly distributed among seven chromosomes were identified from the barley (cv. Morex) genome. Phylogenetic analysis categorized them into 18 subfamilies. They contained combinations of 21 domains and consisted of 3 to 34 exons. Evolution analysis revealed that segmental duplication contributed predominantly to the expansion of the family in barley, and the duplicated gene pairs have undergone purifying selection. About eight hundred Snf2 family genes were identified from 20 barley accessions, ranging from 38 to 41 genes in each. Most of these genes were subjected to purification selection during barley domestication. Most were expressed abundantly during spike development. This study provides a comprehensive characterization of barley Snf2 family members, which should help to improve our understanding of their potential regulatory roles in barley spike development.

SUMMARY: Floral morphology varies considerably between dicots and monocots. The ABCDE model explaining how floral organ development is controlled was formulated using core eudicots and applied to grass crops. Barley (Hordeum. vulgare) has unique floral morphogenesis. Wild barley (H. vulgare ssp. spontaneum), which is the immediate ancestor of cultivated barley (H. vulgare ssp. vulgare), contains a rich reservoir of genetic diversity. However, the wild barley genes involved in floral organ development are still relatively uncharacterized. In this study, we generated an organ‐specific transcriptome atlas for wild barley floral organs. Genome‐wide transcription profiles indicated that 22 838 protein‐coding genes were expressed in at least one organ. These genes were grouped into seven clusters according to the similarities in their expression patterns. Moreover, 5619 genes exhibited organ‐enriched expression, 677 of which were members of 47 transcription factor families. Gene ontology analyses suggested that the functions of the genes with organ‐enriched expression influence the biological processes in floral organs. The co‐expression regulatory network showed that the expression of 690 genes targeted by MADS‐box proteins was highly positively correlated with the expression of ABCDE model genes during floral morphogenesis. Furthermore, the expression of 138 genes was specific to the wild barley OUH602 genome and not the Morex genome; most of these genes were highly expressed in the glume, awn, lemma, and palea. This study revealed the global gene expression patterns underlying floral morphogenesis in wild barley. On the basis of the study findings, a molecular mechanism controlling floral morphology in barley was proposed.

In early spring 2018, significant mosaic disease symptoms were observed for the first time on barley leaves (Hordeum vulgare L., cv. New Sachiho Golden) in Takanezawa, Tochigi Prefecture, Japan. This cultivar carries the resistance gene rym3 (rym; resistance to yellow mosaic). Through RNA-seq analysis, Barley yellow mosaic virus (BaYMV-Takanezawa) was identified in the roots of all five plants (T01–T05) in the field. Phylogenetic analysis of RNA1, encompassing known BaYMV pathotypes I through V, revealed that it shares the same origin as isolate pathotype IV (BaYMV-Ohtawara pathotype). However, RNA2 analysis of isolates revealed the simultaneous presence of two distinct BaYMV isolates, BaYMV-Takanezawa-T01 (DRR552862, closely related to pathotype IV) and BaYMV-Takanezawa-T02 (DRR552863, closely related to pathotype III). The amino acid sequences of the BaYMV-Takanezawa isolates displayed variations, particularly in the VPg and N-terminal region of CP, containing mutations not found in other domains of the virus genome. Changes in the CI (RNA1 amino acid residue 459) and CP (RNA1 amino acid residue 2138) proteins correlated with pathogenicity. These findings underscore the importance of monitoring and understanding the genetic diversity of BaYMV for effective disease management strategies in crop breeding.

Various members of the viral genera Furovirus and Bymovirus are damaging pathogens of a range of crop species. Infection of the soil‐borne plasmodiophorid Polymyxa graminis transmits both Japanese soil‐borne wheat mosaic virus (JSBWMV) and the barley yellow mosaic virus (BaYMV) to barley, but their interaction during an episode of their co‐infection has not been characterized to date. Here, we present an analysis of the titer of JSBWMV and BaYMV in plants of winter barley growing over a five‐month period from late fall until mid‐spring. Although JSBWMV was detectable in the plants' roots four weeks earlier than BaYMV, the translocation of both viruses from the root to the leaves occurred nearly simultaneously. Both viruses were co‐localized in the roots, leaf sheathes, and leaf blades; however, in some stripes of leaf veins where infection by JSBWMV was prominent, BaYMV was not detectable. A substantial titer of both viruses persisted until early spring, after which JSBWMV became more prominent, being in a range of 10 to 100 times abundant of BaYMV. However, JSBWMV was only able to infect a single wheat accession (cv. Norin 61), whereas all of the wheat entries assayed appeared to be immune to BaYMV infection. Overall, our findings highlight the importance of resistance mechanisms against soil‐borne viruses in cereal crops, expanding our understanding of plant‐virus interactions and potentially informing strategies for crop protection against viral pathogens.