Loss of ADP-glucose transporter in barley sex1 mutant caused shrunken endosperm but with elevated protein and ß-glucan content in whole meal.

Grain shape and plumpness affect barley yield. Despite numerous studies on shrunken endosperm mutants in barley, their molecular mechanism and application potential in the food industry are largely unknown. Here, map-based cloning, co-segregation analyses, and allelic variant validation revealed that the loss of HORVU6Hr1G037950 encoding an ADP-glucose transporter caused the shrunken endosperm in sex1. Haplotype analysis suggested that hap4 in the promoter sequence was positively related to the hundred-grain weight showing a breeding potential. A pair of near-isogenic lines targeting HORVU6Hr1G037950 was produced and characterized to investigate molecular mechanisms that SEX1 regulates endosperm development. Results presented that the absence of the SEX1 gene led to the decrease of starch content and A-type granules size, the increase of ß-glucan, protein, gelatinization temperature, soluble sugar content, amylopectin A chains, and B1 chains. Enzymatic activity, transcriptome and metabolome analyses revealed the loss of SEX1 results in an impaired ADP-glucose-to-starch conversion process, consequently leading to higher soluble sugar contents and lower starch accumulation, thereby inducing a shrunken-endosperm phenotype in sex1. Taken together, this study provides new insights into barley grain development, and the elevated protein and ß-glucan contents of the whole meal in sex1 imply its promising application in the food industry.

Identification and characterization of mRNAs and lncRNAs of a barley shrunken endosperm mutant using RNA-seq.

Barley shrunken endosperm mutants have been extensively reported. However, knowledge of the underlying molecular mechanisms of these mutants remains limited. Here, a pair of near isogenic lines (normal endosperm: Bowman and shrunken endosperm: sex1) was subjected to transcriptome analysis to identify mRNAs and lncRNAs related to endosperm development to further dissect its mechanism of molecular regulation. A total of 2123 (1140 up- and 983 down-regulated) unique differentially expressed genes (DEGs) were detected. Functional analyses showed that these DEGs were mainly involved in starch and sucrose metabolism, biosynthesis of secondary metabolites, and plant hormone signal transduction. A total of 343 unique target genes were identified for 57 differentially expressed lncRNAs (DE lncRNAs). These DE lncRNAs were mainly involved in glycerophospholipid metabolism, starch and sucrose metabolism, hormone signal transduction, and stress response. In addition, key lncRNAs were identified by constructing a co-expression network of the target genes of DE lncRNAs. Transcriptome results suggested that mRNA and lncRNA played a critical role in endosperm development. The shrunken endosperm in barley seems to be closely related to plant hormone signal transduction, starch and sucrose metabolism, and cell apoptosis. This study provides a foundation for fine mapping, elucidates the molecular mechanism of shrunken endosperm mutants, and also provides a reference for further studies of lncRNAs during the grain development of plants.

Quantitative trait loci for seeding root traits and the relationships between root and agronomic traits in common wheat.

A completely developed and vigorous root system can provide a stable platform for aboveground plant organs. To identify loci controlling root traits that could be used in wheat (Triticum aestivum L.) breeding, 199 recombinant inbred lines were used to measure and analyze eight root traits. A total of 18 quantitative trait loci (QTL) located on chromosomes 1A, 2A, 2B, 2D, 4B, 4D, 6A, 7A, and 7B were identified. The phenotypic variation explained by these 18 QTL ranged from 3.27% to 11.75%, and the logarithm of odds scores ranged from 2.50 to 6.58. A comparison of physical intervals indicated several new QTL for root traits were identified. In addition, significant correlations between root and agronomic traits were detected and discussed. The results presented in this study, along with those of previous reports, suggest that chromosomes 2 and 7 likely play important roles in the growth and development of wheat roots.

Correction to: Identification and validation of a major and stably expressed QTL for spikelet number per spike in bread wheat.

Unfortunately, the author contribution statement was missed out in the original publication. The complete statement is given below.

Identification of quantitative trait loci for kernel traits in a wheat cultivar Chuannong16.

BACKGROUND: Kernel length (KL), kernel width (KW) and thousand-kernel weight (TKW) are key agronomic traits in wheat breeding. Chuannong16 ('CN16') is a commercial cultivar with significantly longer kernels than the line '20828'. To identify and characterize potential alleles from CN16 controlling KL, the previously developed recombinant inbred line (RIL) population derived from the cross '20828' × 'CN16' and the genetic map constructed by the Wheat55K SNP array and SSR markers were used to perform quantitative trait locus/loci (QTL) analyses for kernel traits. RESULTS: A total of 11 putative QTL associated with kernel traits were identified and they were located on chromosomes 1A (2 QTL), 2B (2 QTL), 2D (3 QTL), 3D, 4A, 6A, and 7A, respectively. Among them, three major QTL, QKL.sicau-2D, QKW.sicau-2D and QTKW.sicau-2D, controlling KL, KW and TKW, respectively, were detected in three different environments. Respectively, they explained 10.88-18.85%, 17.21-21.49% and 10.01-23.20% of the phenotypic variance. Further, they were genetically mapped in the same interval on chromosome 2DS. A previously developed kompetitive allele-specific PCR (KASP) marker KASP-AX-94721936 was integrated in the genetic map and QTL re-mapping finally located the three major QTL in a 1- cM region flanked by AX-111096297 and KASP-AX-94721936. Another two co-located QTL intervals for KL and TKW were also identified. A few predicted genes involved in regulation of kernel growth and development were identified in the intervals of these identified QTL. Significant relationships between kernel traits and spikelet number per spike and anthesis date were detected and discussed. CONCLUSIONS: Three major and stably expressed QTL associated with KL, KW, and TKW were identified. A KASP marker tightly linked to these three major QTL was integrated. These findings provide information for subsequent fine mapping and cloning the three co-localized major QTL for kernel traits.

Identification and validation of a major and stably expressed QTL for spikelet number per spike in bread wheat.

KEY MESSAGE: A major and stably expressed QTL for spikelet number per spike identified in a 2-cM interval on chromosome arm 2DS was validated using two populations with different genetic backgrounds. Spikelet number per spike (SNS) plays a key role in wheat yield improvement. Numerous genetic and environmental factors influencing SNS have been documented, but the number of major, stably expressed and validated loci underlying SNS is still limited. In this study, a recombinant inbred line (RIL) population derived from a normal spikelet cultivar and a multiple-spikelet wheat line (with a longer spike with more canonically oriented apical spikelets) was genotyped using a Wheat55K single-nucleotide polymorphism (SNP) array and simple sequence repeat (SSR) markers. SNS was measured for this RIL population in eight environments. Five QTL were each identified in two or more environments. One of them, QSns.sau-2D (LOD = 3.47-38.24, PVE = 10.16-45.68%), was detected in all the eight environments. The QTL was located in a 2-cM interval on chromosome arm 2DS flanked by the markers AX-109836946 and AX-111956072. This QTL, QSns.sau-2D, significantly increased SNS by up to 14.72%. Several genes associated with plant growth and development were identified in the physical interval of QSns.sau-2D. This QTL was further validated by the tightly linked Kompetitive Allele Specific PCR (KASP) marker, KASP-AX-94721936, in two other populations with different genetic backgrounds. The significant correlation between SNS and anthesis date, plant height, spike length, grain number per spike and thousand-grain weight were detected and discussed. These results lay the foundation for fine mapping and cloning gene(s) underlying QSns.sau-2D.