New QTL alleles for quality-related traits in spring wheat revealed by RIL population derived from supernumerary × non-supernumerary spikelet genotypes.

KEY MESSAGE: A population developed from an exotic line with supernumerary spikelets was genetically dissected for eight quality traits, discovering new genes/alleles with potential use in wheat breeding programs. Identifying new QTLs and alleles in exotic germplasm is paramount for further improvement of quality traits in wheat. In the present study, an RIL population developed from a cross of an elite wheat line (WCB414) and an exotic genotype with supernumerary spikelets (SS) was used to identify QTLs and new alleles for eight quality traits. Composite interval mapping for 1,000 kernels weight (TKW), kernel volume weight (KVW), grain protein content (GPC), percent of flour extraction (FE) and four mixograph-related traits identified a total of 69 QTLs including 19 stable QTLs. These QTLs were located on 18 different chromosomes (except 4D, 5D, and 6D). Thirteen of these QTLs explained more than 15% of phenotypic variation (PV) and were considered as major QTLs. In this study, we identified 11 QTLs for TKW (R (2) = 7.2-17.1 %), 10 for KVW (R (2) = 6.7-22.5%), 11 for GPC (R (2) = 4.7-16.9%), 6 for FE (R (2) = 4.8-19%) and 31 for mixograph-related traits (R (2) = 3.2-41.2%). In this population, several previously identified QTLs for SS, nine spike-related and ten agronomic traits were co-located with the quality QTLs, suggesting pleiotropic effects or close linkage among loci. The traits GPC and mixogram-related traits were positively correlated with SS. Indeed, several loci for quality traits were co-located with QTL for SS. The exotic parent contributed positive alleles that increased PV of the traits at 56% of loci demonstrating the suitability of germplasm with SS to improve quality traits in wheat.

Colocalization of sucrose synthase expression and sucrose storage in the sugarbeet taproot indicates a potential role for sucrose catabolism in sucrose accumulation.

Sucrose metabolism is believed to have a central role in promoting sink strength and sucrose storage in the sugarbeet taproot. How sucrose accumulation is increased by sucrose-degrading enzymes, however, is a paradox. To elucidate roles for sucrose-degrading activities in sucrose accumulation, relationships between the intercellular location of sucrose-catabolizing enzymes and sites of sucrose accumulation were determined in the sugarbeet taproot. Sucrose storage was evident in parenchyma cells of the outer cortex, rays, and rings of parenchyma tissue, but was absent in phloem, the vascular cambium, cells surrounding these tissues, or cells surrounding xylem. Sucrose synthase, which was primarily responsible for sucrose catabolism throughout the taproot, was expressed in similar cell and tissue types to those accumulating sucrose. Colocalization of sucrose synthase with sucrose accumulation, as well as sucrose synthase localization near the tonoplast, suggests a role for the enzyme in generating metabolic energy to fuel sucrose sequestration in the vacuole. Localization near the plasma membrane also suggests a role for sucrose synthase in supplying substrates for cell wall biosynthesis. By utilizing sucrose for ATP or cell wall biosynthesis, sucrose synthase likely maintains the source-to-sink sucrose gradient that drives sucrose transport into the root, thereby promoting sugarbeet root sink strength.

Glycolysis Is Dynamic and Relates Closely to Respiration Rate in Stored Sugarbeet Roots.

Although respiration is the principal cause of the loss of sucrose in postharvest sugarbeet (Beta vulgaris L.), the internal mechanisms that control root respiration rate are unknown. Available evidence, however, indicates that respiration rate is likely to be controlled by the availability of respiratory substrates, and glycolysis has a central role in generating these substrates. To determine glycolytic changes that occur in sugarbeet roots after harvest and to elucidate relationships between glycolysis and respiration, sugarbeet roots were stored for up to 60 days, during which activities of glycolytic enzymes and concentrations of glycolytic substrates, intermediates, cofactors, and products were determined. Respiration rate was also determined, and relationships between respiration rate and glycolytic enzymes and metabolites were evaluated. Glycolysis was highly variable during storage, with 10 of 14 glycolytic activities and 14 of 17 glycolytic metabolites significantly altered during storage. Changes in glycolytic enzyme activities and metabolites occurred throughout the 60 day storage period, but were greatest in the first 4 days after harvest. Positive relationships between changes in glycolytic enzyme activities and root respiration rate were abundant, with 10 of 14 enzyme activities elevated when root respiration was elevated and 9 glycolytic activities static during periods of unchanging respiration rate. Major roles for pyruvate kinase and phosphofructokinase in the regulation of postharvest sugarbeet root glycolysis were indicated based on changes in enzymatic activities and concentrations of their substrates and products. Additionally, a strong positive relationship between respiration rate and pyruvate kinase activity was found indicating that downstream TCA cycle enzymes were unlikely to regulate or restrict root respiration in a major way. Overall, these results establish that glycolysis is not static during sugarbeet root storage and that changes in glycolysis are closely related to changes in sugarbeet root respiration.

Short- and long-term changes in sugarbeet (Beta vulgaris L.) gene expression due to postharvest jasmonic acid treatment - Data.

Jasmonic acid is a natural plant hormone that induces native defense responses in plants. Sugarbeet (Beta vulgaris L.) root unigenes that were differentially expressed 2 and 60 days after a postharvest jasmonic acid treatment are presented. Data include changes in unigene expression relative to water-treated controls, unigene annotations against nonredundant (Nr), Swiss-Prot, Clusters of Orthologous Groups (COG), and Kyoto Encyclopedia of Genes and Genomes (KEGG) protein databases, and unigene annotations with Gene Ontology (GO) terms. Putative defense unigenes are compiled and annotated against the sugarbeet genome. Differential gene expression data were generated by RNA sequencing. Interpretation of the data is available in the research article, "Jasmonic acid causes short- and long-term alterations to the transcriptome and the expression of defense genes in sugarbeet roots" (K.K. Fugate, L.S. Oliveira, J.P. Ferrareze, M.D. Bolton, E.L. Deckard, F.L. Finger, 2017) [1]. Public dissemination of this dataset will allow further analyses of the data.

Cold Temperature Delays Wound Healing in Postharvest Sugarbeet Roots.

Storage temperature affects the rate and extent of wound-healing in a number of root and tuber crops. The effect of storage temperature on wound-healing in sugarbeet (Beta vulgaris L.) roots, however, is largely unknown. Wound-healing of sugarbeet roots was investigated using surface-abraded roots stored at 6 and 12°C for 28 days. Surface abrasions are common injuries of stored roots, and the storage temperatures used are typical of freshly harvested or rapidly cooled roots. Transpiration rate from the wounded surface and root weight loss were used to quantify wound healing. At 12°C, transpiration rate from the wounded surface declined within 14 days and wounded roots lost weight at a rate similar to unwounded controls. At 6°C, transpiration rate from the wounded surface did not decline in the 28 days after injury, and wounded roots lost 44% more weight than controls after 28 days storage. Melanin formation, lignification, and suberization occurred more rapidly at 12°C than at 6°C, and a continuous layer of lignified and suberized cells developed at 12°C, but not at 6°C. Examination of enzyme activities involved in melanin, lignin, and suberin formation indicated that differences in melanin formation at 6 and 12°C were related to differences in polyphenol oxidase activity, although no relationships between suberin or lignin formation and phenylalanine ammonia lyase or peroxidase activity were evident. Wound-induced respiration was initially greater at 12°C than at 6°C. However, with continued storage, respiration rate of wounded roots declined more rapidly at 12°C, and over 28 days, the increase in respiration due to injury was 52% greater in roots stored at 6°C than in roots stored at 12°C. The data indicate that storage at 6°C severely slowed and impaired wound-healing of surface-abraded sugarbeet roots relative to roots stored at 12°C and suggest that postharvest losses may be accelerated if freshly harvested roots are cooled too quickly.

Genome-Wide Mapping of Spike-Related and Agronomic Traits in a Common Wheat Population Derived from a Supernumerary Spikelet Parent and an Elite Parent.

In wheat, exotic genotypes harbor a broad range of spike-related traits, and can be used as a source of new genes for germplasm enhancement in wheat breeding programs. In the present study, a population of 163 recombinant inbred lines was derived from a cross between an elite line (WCB414) and an exotic line (WCB617) with branched spike (supernumerary spikelet; SS) head morphology. The population was evaluated over four to six environments to identify quantitative trait loci (QTL) associated with nine spike-related traits and 10 agronomic traits. A genetic map consisting of 939 diversity arrays technology (DArT) markers was constructed. Composite interval mapping identified a total of 143 QTL located on 17 different wheat chromosomes and included 33 consistent and definitive QTL. The amount of phenotype variation explained (PVE) by individual QTL ranged from 0.61 to 91.8%. One major QTL for glume pubescence was located in a QTL-rich region on the short arm of chromosome 1A, where loci for other traits such as for kernels per spike (KS) and spike length (SL) were also identified. Similarly, a cluster of QTL associated with yield-related, agronomic and spike-related traits contributing up to 40.3% of PVE was found on the short arm of chromosome 2D, in the vicinity of a major QTL for SS-related traits. Consistent and major QTL identified in the present study may be useful in marker-assisted breeding programs to facilitate transfer of desirable alleles into other germplasm. Desirable QTL alleles were also contributed by the exotic line, suggesting the possibility of enriching the breeding germplasm with alleles from SS genotypes.