Sugary Enhancer Research Articles

The sugary enhancer1 (se1) Allele Is Associated with Significant Decreases in Carotenoids and Tocotrienols in Yellow (Y1) sugary1 (su1) Sweet Corn

A distinctive phenotype of homozygous sugary enhancer1 (se1) sweet corn (Zea mays) inbreds and hybrids is a light-yellow color in mature kernels. Carotenoid pigments contribute to yellow endosperm color in maize and are of nutritional importance in the human diet along with the related tocochromanols, the E vitamins. Tocochromanols, including both tocopherols and tocotrienols, are antioxidants important in human nutrition and cardiovascular health. Effects of the presence of sugary enhancer1 allele on carotenoid and tocochromanol levels in homozygous su1, Y1 endosperm were evaluated in the Wisconsin Sweet Corn Diversity Panel. Although population structure was present in the panel, the majority of variation in carotenoid levels was explained by genotype at the se1 locus. se1 was associated with significant decreases in the amount of lutein (34%) and zeaxanthin (36%) and decreases of tocotrienols by 12% to 65%. There were no significant differences in β-carotene and tocopherol levels between the two groups. Given that the biosynthesis pathways for carotenoids and tocochromanols are well defined, these differences in carotenoids and tocotrienols between su1Se1 and su1se1 inbreds point to a broader role of se1 alleles in metabolic pathways beyond endosperm starch production.

Central Roles of ZmNAC128 and ZmNAC130 in Nutrient Uptake and Storage during Maize Grain Filling.

Grain filling is critical for determining yield and quality, raising the question of whether central coordinators exist to facilitate the uptake and storage of various substances from maternal to filial tissues. The duplicate NAC transcription factors ZmNAC128 and ZmNAC130 could potentially serve as central coordinators. By analyzing differentially expressed genes from zmnac128 zmnac130 mutants across different genetic backgrounds and growing years, we identified 243 highly and differentially expressed genes (hdEGs) as the core target genes. These 243 hdEGs were associated with storage metabolism and transporters. ZmNAC128 and ZmNAC130 play vital roles in storage metabolism, and this study revealed two additional starch metabolism-related genes, sugary enhancer1 and hexokinase1, as their direct targets. A key finding of this study was the inclusion of 17 transporter genes within the 243 hdEGs, with significant alterations in the levels of more than 10 elements/substances in mutant kernels. Among them, six out of the nine upregulated transporter genes were linked to the transport of heavy metals and metalloids (HMMs), which was consistent with the enrichment of cadmium, lead, and arsenic observed in mutant kernels. Interestingly, the levels of Mg and Zn, minerals important to biofortification efforts, were reduced in mutant kernels. In addition to their direct involvement in sugar transport, ZmNAC128 and ZmNAC130 also activate the expression of the endosperm-preferential nitrogen and phosphate transporters ZmNPF1.1 and ZmPHO1;2. This coordinated regulation limits the intake of HMMs, enhances biofortification, and facilitates the uptake and storage of essential nutrients.

Genetic Perturbation of the Starch Biosynthesis in Maize Endosperm Reveals Sugar-Responsive Gene Networks.

In maize, starch mutants have facilitated characterization of key genes involved in endosperm starch biosynthesis such as large subunit of AGPase Shrunken2 (Sh2) and isoamylase type DBE Sugary1 (Su1). While many starch biosynthesis enzymes have been characterized, the mechanisms of certain genes (including Sugary enhancer1) are yet undefined, and very little is understood about the regulation of starch biosynthesis. As a model, we utilize commercially important sweet corn mutations, sh2 and su1, to genetically perturb starch production in the endosperm. To characterize the transcriptomic response to starch mutations and identify potential regulators of this pathway, differential expression and coexpression network analysis was performed on near-isogenic lines (NILs) (wildtype, sh2, and su1) in six genetic backgrounds. Lines were grown in field conditions and kernels were sampled in consecutive developmental stages (blister stage at 14 days after pollination (DAP), milk stage at 21 DAP, and dent stage at 28 DAP). Kernels were dissected to separate embryo and pericarp from the endosperm tissue and 3′ RNA-seq libraries were prepared. Mutation of the Su1 gene led to minimal changes in the endosperm transcriptome. Responses to loss of sh2 function include increased expression of sugar (SWEET) transporters and of genes for ABA signaling. Key regulators of starch biosynthesis and grain filling were identified. Notably, this includes Class II trehalose 6-phosphate synthases, Hexokinase1, and Apetala2 transcription factor-like (AP2/ERF) transcription factors. Additionally, our results provide insight into the mechanism of Sugary enhancer1, suggesting a potential role in regulating GA signaling via GRAS transcription factor Scarecrow-like1.

Morpho-biological traits and productivity of lines and hybrids of super sweet corn obtained on the basis of sh2 mutation

Purpose. Super sweet corn contains a gene that, being expressed leads to an increase in the concentration of sugar. Endosperm genes that regulate the increase in sugar content and decrease in starch content were identified; the most effective of them were shrunken2 (sh2), brittle1 (bt), sugary1 (su1) and sugary enhancer1 (se). The recessive mutation of shrunken2 (sh2) provides a high content of sugars in the grain of milk-wax ripeness compared to other mutant forms that directly affects the taste of sh2-hybrids causes widespread use of this mutation in breeding and has the greatest commercial potential. The main task of breeding is to create a new generation of high-yielding hybrids; it depends on the availability of high-quality source breeding material. Therefore, the aim of our work was the assessment of morpho-biological traits of the super sweet corn lines, selection of the best donor lines of genetic traits, creating of high-yielding corn hybrids.Methods. Morpho-biological traits of the studied lines were evaluated according to the Classifier – handbook of Zea mays L. Comprehensive analysis of samples on economically valuable traits was carried out in accordance with the Methodical recommendations for field and laboratory study of genetic resources of corn. The content of reducing sugars in the grain of the studied corn lines and hybrids was determined by Bertrand method.Results. A study of morpho-biological traits of super sweet corn was carried out. Significant differences between the studied lines were observed in the vegetation period duration, the number of grains in one row and the number of grain rows in the cob. The lines-sources of economically valuable features that can be used for practical selection were identified. Crossing was carried out and 50 hybrid combinations were obtained; among them 16 hybrids cha­racterized by the best levels of economic characteristics were selected.Conclusions. As a result of the analysis of the main morpho-biological traits in hybrid combinations of super sweet corn with the mutant sh2 gene, the sources of selection-valuable traits were identified. According to the vegetation period, all lines were divided into three groups: early – 8 lines, middle – 6 and late – 8 ones. It was determined that promising donors of cob productivity were SH-621, SH-234 and SH-936 lines; signs of plant height – SH-234 and SH-936, number of grain rows – SH-234 and SH-113, cob lengths – SH-318 and SH-936. According to the results of studies of morpho-biological traits, the best lines were identified. They were crossed with other lines of super sweet corn and hybrids were obtained. The three best of them, ‘Matir Drakoniv F1’, ‘Yurmala F1’ and ‘Larus F1’, were submitted for state registration.

Maize sugary enhancer1 (se1) is a gene affecting endosperm starch metabolism

sugary enhancer1 (se1) is a naturally occurring mutant allele involved in starch metabolism in maize endosperm. It is a recessive modifier of sugary1 (su1) and commercially important in modern sweet corn breeding, but its molecular identity and mode of action remain unknown. Here, we developed a pair of near-isogenic lines, W822Gse (su1-ref/su1-ref se1/se1) and W822GSe (su1-ref/su1-ref Se1/Se1), that Mendelize the se1 phenotype in an su1-ref background. W822Gse kernels have lower starch and higher water soluble polysaccharide and sugars than W822GSe kernels. Using high-resolution genetic mapping, we found that wild-type Se1 is a gene Zm00001d007657 on chromosome 2 and a deletion of this gene causes the se1 phenotype. Comparative metabolic profiling of seed tissue between these 2 isolines revealed the remarkable difference in carbohydrate metabolism, with sucrose and maltose highly accumulated in the mutant. Se1 is predominantly expressed in the endosperm, with low expression in leaf and root tissues. Differential expression analysis identified genes enriched in both starch biosynthesis and degradation processes, indicating a pleiotropic regulatory effect of se1 Repressed expression of Se1 and Su1 in RNA interference-mediated transgenic maize validates that deletion of the gene identified as Se1 is a true causal gene responsible for the se1 phenotype. The findings contribute to our understanding of starch metabolism in cereal crops.

A Common Genetic Basis for Cross-sensitivity to Mesotrione and Nicosulfuron in Sweet Corn Hybrid Cultivars and Inbreds Grown throughout North America

Mutation of a cytochrome P450 (CYP) gene on the short arm of chromosome five, referred to as nsf1 or ben1, conditions sensitivity to certain P450-metabolized herbicides in corn (Zea mays L.). Previous research has shown that the sweet corn inbred Cr1 is sensitive to nicosulfuron, mesotrione, and at least seven other P450-metabolized herbicides with five different modes of action. Although the nsf1/ben1 CYP gene has not been sequenced from Cr1, a QTL that conditions cross-sensitivity to P450-metabolized herbicides was detected in a segregating population of Cr1 × Cr2 (herbicide tolerant) on the short arm chromosome five in tight linkage disequilibrium with the nsf1/ben1 CYP locus. Sweet corn hybrid cultivars and inbreds that had been identified in previous research as being susceptible to injury from P450-metabolized herbicides were tested in this study to determine if they were allelic with Cr1 for cross-sensitivity to nicosulfuron and mesotrione. These cultivars and inbreds were developed by 12 independent commercial breeding programs. These cultivars include sugary, sugary enhancer, and shrunken-2 endosperm types that are grown for processing and fresh consumption in markets throughout North America and in other temperate climates throughout the world. Each hybrid cultivar, their F2 progeny, and progeny from testcrosses of cultivars with Cr1 and Cr2 were evaluated for responses to mesotrione and nicosulfuron. Each inbred line, progeny from crosses of inbreds with Cr1 and Cr2, and F2 progeny from crosses of inbreds with Cr1 were also tested. Based on segregation of progeny from testcrosses with Cr1 and Cr2 and the F2 generation, 45 sweet corn hybrid cultivars and 29 sweet corn inbreds, including lines from each of the 12 breeding programs, appeared to be sensitive to nicosulfuron and mesotrione as the result of a gene that is the same as or very closely linked to the gene in Cr1. None of the cultivars or inbreds appeared to be sensitive to these herbicides as a result of other independent genes; however, additional genes that modify responses to these herbicides may be present in a few cases. The presence of a gene conditioning sensitivity to nicosulfuron and mesotrione, and probably to several other P450-metablolized herbicides, provides an explanation for varied levels of injury and inconsistent responses of sweet corn hybrid cultivars under differing environmental conditions. This information provides a basis from which an industry-wide concern with herbicide sensitivity in sweet corn can be addressed by various methods, including the elimination of an allele rendering germplasm sensitive.

Reciprocal Differences in Sugary × Sugary Enhancer Sweet Corn Hybrids

Reciprocal effects in sugary × sugary enhancer hybrids of sweet corn (Zea mays L.) have been only reported for sugar content and in a very limited number of hybrids and have not been determined for agronomic traits. By evaluating 34 sugary × sugary enhancer hybrids with reciprocals in three environments, the main objectives of this work were, for agronomic and quality traits, to determine the presence or absence of reciprocal differences in the sugary × sugary enhancer hybrids, to study the interest of using sugary inbreds as seed parents of the sugary × sugary enhancer hybrids, and to determine if reciprocal differences are interacting with different genetic backgrounds and different environments. For agronomic traits as emergence, early vigor, and silking date, significant (P ≤ 0.05) reciprocal differences were found in many of the sugary × sugary enhancer hybrids, but for quality traits, significant (P ≤ 0.05) reciprocal differences were only found in a few hybrids. The sugary lines as seed parents of the crosses tended to have on average a favorable effect on agronomic traits, but this was only considerable in some environmental conditions. The difference between the sugary and sugary enhancer lines as seed parent of the crosses was strongly influenced by the genetic background.

Agronomic performance of sweetcorn populations derived from crosses between sweetcorn and field corn

The adaptation of sweetcorn (Zea mays L.) to Spanish growing conditions needs to be improved, something that could be achieved by incorporating traits from field corn populations. The aim of the present study was to analyse the performance of sweetcorn populations carrying the genes sugary1 (su1) or shrunken2 (sh2), as well as sugary enhancer double mutants (su1 se1), produced by crosses between sweetcorn donor populations and the Spanish field corn populations Lazcano, Oroso and Rastrojero. The three field corn populations plus the su1, su1 se1 and sh2 populations derived from them, as well as the su1, su1 se1, and sh2 donor populations used in the crosses with the field corn populations, were evaluated for their agronomic performance. Several hybrids were used as controls. Assessments were made in Zaragoza (NE Spain) and Pontevedra (NW Spain) over two years. The ability of the field corn populations to improve the sweetcorn varieties was not greatly affected by the sweetcorn mutant involved. The field corn populations chosen as donors for improving sweetcorn must depend on the growing conditions in mind. Sweetcorn populations derived Oroso would appear to be the most favourable for northern Spain, while those derived from Rastrojero would appear to be the most suitable for inland Spain, although other field corn populations are still to be examined.

Hybrids sugary × sugary enhancer of sweet corn: A valuable option for cool environments

Sugary ( Se1Se1) sweet corn hybrids do not have a high quality for human consumption according to the preferences of today's consumers, although they have a good stand establishment in cool environments. On the contrary, sugary enhancer (s e1se1) hybrids have a high table quality, but a poor stand establishment in areas with a cool growing season. Sugary × sugary enhancer ( Se1se1) sweet corn genotypes could be a valuable alternative for cool environments, but no information is available about the performance of sugary × sugary enhancer hybrids under such conditions. The objective of this paper is to evaluate the potential of sugary × sugary enhancer sweet corn genotypes in cool environments in comparison with sugary and sugary enhancer genotypes. Eight sugary lines and eight sugary enhancer lines were used as the parental lines of 15 sugary, 12 sugary enhancer, and 57 sugary × sugary enhancer hybrids that were evaluated in three different cool environments. The results of this work show that sweet corn cultivars with the Se1se1 genotype are an appropriate alternative for cool areas because they have better plant and ear types and a better eating quality than the Se1Se1 genotypes, and better emergence, early vigor, and shorter flowering time than se1se1 genotypes.

Variation of sugary1 and shrunken2 gene frequency in different maize genetic backgrounds

AbstractGenotypes affect the survival of mutant genes in segregating populations. This study elucidates the effect of different maize genetic backgrounds on variation in gene frequency in sweet corn, sugary1 (su1) and sugary enhancer1 (se1), and supersweet corn, shrunken2 (sh2). Four sweet corn inbred lines and a supersweet synthetic were crossed to six field corn inbreds from diverse heterotic groups. The crosses were self‐pollinated and the F2 population was recombined twice. Gene frequencies were calculated from grain frequencies. Variation of su1 frequency differed significantly from random drift and a significant linear reduction was observed for half of the su1su1Se1Se1Sh2Sh2 × Su1Su1Se1Se1Sh2Sh2 crosses. The su1 and sh2 frequencies suffered a significant linear reduction for most su1su1se1se1Sh2Sh2 × Su1Su1Se1Se1Sh2Sh2 and Su1Su1Se1Se1sh2sh2 × Su1Su1Se1Se1Sh2Sh2 crosses, respectively. Also, the residual sums of squares, due to deviations from the linear trend, were significant for some crosses due to frequency‐dependent selection and genotypic interactions. Viability of su1 and sh2 depended on the specific sweet × field corn genotype combination but was not related to field corn heterotic groups. The se1 gene could have a detrimental effect on su1 viability.

Sugary enhancer1 Inbreds to Improve the Quality of Sugary1 Hybrids of Sweet Corn

The better emergence and seedling vigor of sweet corn (Zea mays L.) hybrids homozygous for the gene sugary1 (su1) make them more suitable for cultivation under European Atlantic conditions (cold, wet spring) than those homozygous for other traits. Elite sweet corn inbreds homozygous for both su1 and sugary enhancer1 (se1) could improve the table quality of su1 hybrids. The su1se1 inbreds for improving su1su1 hybrid performance can be chosen in several ways. The aim of this paper was to identify donors among su1se1 inbreds that might improve the quality of su1 hybrids. Eight su1se1 inbreds were crossed with eight su1 inbreds that were parents of fifteen su1 hybrids. Hybrids and inbreds were cultivated next to one another in two locations in northwestern Spain in 1999 and 2000. Several possible estimators for identifying su1se1 inbred donors with favorable alleles lacking in the su1 hybrid were determined. These estimators included the relative number of favorable alleles present in the donor but absent in the hybrid (μǴ), predicted three-way cross (PTC), minimum upper bound (UBND), net improvement (NI), probability of the net gain of favorable alleles when there is complete dominance (PNGg), probability of the net gain of favorable alleles when there is partial dominance or epistasis (PNGceg), and general combining ability (GCA). μǴ and NI were chosen for improving hybrid table quality. These estimators indicate that table quality and other traits of su1 hybrids can be improved by using germplasm from the su1se1 inbred lines. The best donor of quality for most of the hybrids was the inbred line IL731a.

Current models for starch synthesis and the sugary enhancer1 ( se1) mutation in Zea mays

Among the desirable quality traits essential for commercial production of fresh or processed sweet corn, kernel sugar content is universally important. In sweet corn genotypes the primary kernel sugar is sucrose, which is elevated at the expense of starch, particularly amylopectin. Sweet corn mutations have been traditionally divided into two classes. Generally speaking, class one mutations affect cytosolic reactions early in the process of starch synthesis, before starch is synthesized, and class two mutations affect reactions within the amyloplast directly involving starch granule assembly. Two widely used but previously unclassified mutations are sugary1 ( su1) and sugary enhancer1 ( se1). The se1 gene is a recessive modifier of su1; therefore, both genes require mutual discussion. This review provides current information about the su1 and se1 maize endosperm mutations and describes evidence further supporting previous suggestions that they fit criteria for categorization as class two mutants [Science 151 (1966) 341]. Information on the genetics and phenotype of se1 will be summarized and the hypothesized role of the se1 gene product discussed within the context of current models for starch synthesis in Zea mays L.

QTL Influencing Kernel Chemical Composition and Seedling Stand Establishment in Sweet Corn with the shrunken2 and sugary enhancer1 Endosperm Mutations

This study was conducted to identify the chromosomal location and magnitude of effect of quantitative trait loci (QTL) controlling sweet corn (Zea mays L.) stand establishment and investigate the impact of dry kernel characteristics on seedling emergence under field conditions. Genetic and chemical analysis was performed on two F2:3 populations (one homozygous for su1 and segregating for se1, the other homozygous for sh2 endosperm carbohydrate mutations) derived from crosses between parental inbreds that differed in field emergence and kernel chemical composition. A series of restriction fragment-length polymorphism (RFLP) and phenotypic markers distributed throughout the sweet corn genome were used to construct a genetic linkage map for each population. F2:3 families from the two populations were evaluated for seedling emergence and growth rate at four locations. Mature dry kernels of each family were assayed for kernel chemical and physiological parameters. Composite interval analysis revealed significant QTL associations with emergence and kernel chemical and physiological variables. Improved emergence was positively correlated with lower seed leachate conductivity, greater embryo dry weight, and higher kernel starch content. QTL affecting both field emergence and kernel characteristics were detected in both populations. In the su1 se1 population genomic regions significantly influencing emergence across all four environments were found associated with the se1 gene on chromosome 2 and the RFLP loci php200020 on chromosome 7 and umc160 on chromosome 8. In the sh2 population the RFLP loci umc131 on chromosome 2 and bnl9.08 on chromosome 8 were linked to QTL significantly affecting emergence. Since seedling emergence and kernel sugar content have been shown to be negatively correlated, undesirable effects on sweet corn eating quality associated with each emergence QTL is discussed. Segregating QTL linked to RFLP loci in these populations that exert significant effects on the studied traits are candidates for molecular marker-assisted selection to improve sweet corn seed quality.

Comparison of Phenotypic and Marker‐Assisted Selection for Quantitative Traits in Sweet Corn

This investigation was designed to empirically compare the efficiency of marker‐assisted selection (MAS) and phenotypic selection (PS) in enhancing economically important quantitative traits in sweet corn (Zea mays L.). Marker‐assisted selection and PS were applied to three F2:3 base populations (C0) with either the sugary1 (su1), sugary enhancer1 (se1), or shrunken2 (sh2) endosperm mutations. One cycle of selection was applied for both single and multiple traits including seedling emergence, kernel sucrose concentration, kernel tenderness, and hedonic rating (taste panel preference). Twenty percent of the families in each of the base populations were selected and intermated to constitute MAS‐ and PS‐based C1 composite populations. Selection efficiencies were evaluated on the basis of gains over one cycle and estimated evaluation costs. A total of 52 paired comparisons were made between MAS and PS composite populations. In 38% of the paired comparisons, MAS resulted in significantly higher gain than PS across the three C1 composite populations, while PS was significantly greater in only 4% of the cases. The average MAS and PS gain across all composite populations and selected traits, calculated as percent increase or decrease from the randomly selected controls, was 10.9% and 6.1%, respectively. Use of MAS is most appropriate when traits are difficult and costly to measure. However, for some traits, the higher gain from MAS can compensate for the higher costs of MAS. It was concluded that incorporating DNA markers to traditional breeding programs could expedite selection progress and be cost‐effective.

Pre-harvest accumulation of deoxynivalenol in sweet corn ears inoculated with Fusarium graminearum

Three types of commercial sweet corn hybrids [sugary (su1), shrunken or ‘supersweet’ (sh2) and sugary enhancer (se1)] were silk channel inoculated in 1996 and 1997 with a macroconidial suspension of Fusarium graminearum to determine how early the mycotoxin deoxynivalenol accumulates in kernels. Disease symptoms rapidly developed on all hybrids and were apparent 4 days after inoculation. Symptoms stabilized by 28 days after inoculation. Toxin levels were greater than 1 μg/g in kernels as early as 2 weeks after silk emergence and rapidly increased to extremely high levels. Susceptibility in all hybrids decreased as the silk dried out. Deoxynivalenol concentrations were correlated to disease severity. There was some indication that the sh2 genotype was more susceptible than the su1 or se1 genotypes. These results suggest that improvement needs to be made in sweet corn with respect to resistance to gibberella ear rot.

Marker-assisted Selection for Improved Emergence and Eating Quality in Sweet Corn

Marker-assisted selection is proposed to be more effective than phenotypic selection in improving complex traits with low heritability. This study was designed to test empirically the efficiency of marker-assisted selection (MAS) vs. phenotypic selection (PS) in enhancing economically important characters in sweet corn using composite populations consisting of selected F2:3 families from two populations. In previous studies in our laboratory, these segregating populations were developed and assayed for genes influencing sweet corn emergence and eating quality. The 214 F2:3 families in the first population (W678su1 × IL731ase1) were classified into three sub-populations according to segregation for the se1gene. Marker-assisted selection and phenotypic selection were applied on the two homozygous sugary1 and sugary enhancer1 sub-populations separately. The second population consisted of 117 F2:3 families from the cross of Ia453sh2 × IL451bsh2. The genotypic selection was based on the polymorphism of five RFLP markers linked to QTL associated with significant effects on emergence and eating quality in the F2:3 generation. Twenty percent of the families in each population with the highest and lowest genotypic scores and phenotypic performance values were selected to constitute the MAS and PS composites, respectively. Emergence was evaluated in four different environments in Illinois and Wisconsin, while eating quality traits were evaluated in Illinois only. Results for emergence, with relatively high h2, in two out of three populations indicated that marker-assisted selection was superior to phenotypic selection. The effectiveness of MAS on enhancing stand establishment and eating quality will be discussed.

Changes in carbohydrate composition and α-amylase expression during germination and seedling growth of starch-deficient endosperm mutants of maize

Kernels of 28 different maize ( Zea mays L.) genotypes consisting of several inbreds isogenic for the starch-deficient endosperm mutations sugary 1 ( su1), sugary1 sugary enhancer 1 ( su1se1), and shrunken2 ( sh2) were used to study the effect of these mutations on carbohydrate composition and α-amylase expression during germination and seedling growth in comparison to normal starchy kernels ( Su). Sugar (fructose, glucose, sucrose, and maltose), WSP (water-soluble polysaccharide), and insoluble starch contents were determined for endosperm and scutellar tissues for each of the genotypes at four stages of seedling development. While initial levels of endosperm sucrose were higher in the endosperm mutants, they rapidly declined by radicle emergence and remained low thereafter. Mobilization of carbohydrate reserves was most reduced in the sh2 genotypes. Collectively, these factors represent a limited carbon supply for the developing sh2 seedling which may impact seedling vigor. A more significant negative correlation was observed between percentage germination and endosperm sugar content than between percentage germination and scutellar sugar content. High initial levels of endosperm sucrose in the mutants correlate with a severe reduction of α-amylase (EC 3.2.1.1) transcript abundance. The same correlation does not hold for glucose and maltose, as at later stages of germination, levels were significantly higher in the Su genotype while the α-amylase mRNA levels remained high. Furthermore, the ratio of α-amylase enzyme activity to transcript abundance was considerably lower in the sh2 aleurone compared to the Su aleurone at radicle emergence. Genotype specific differences in α-amylase gene expression strongly correlate with endosperm sugar content and composition during germination.

Sugary enhancer1 (se1) Gene Endosperm Dosage and Sweet Corn Carbohydrate Content

Inbreds IL451b sugary1 (su1) and IL678a su1 isogenic for the sugary enhancer1 (se1) gene mutation were used to analyze the relationship between se1 gene dosage and endosperm sugar content. Each line was self-pollinated and reciprocal crosses were made between the isolines of each genotype to produce se1 gene dosages of 0, 1, 2, and 3 in the triploid endosperm. Ears were harvested at 15, 18, 21, 24, 27, and 45 days after pollination (DAP). Whole kernels were freeze-dried, ground into powder, and stored at –80°C until subsequent chemical analyses. Sucrose, glucose and fructose were analyzed using high-pressure liquid chromatography (HPLC), the results of which indicated a significant increase in kernel sugar content when the se1 allele is homozygous. \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[\begin{array}{lcl}&\underline{\mathrm{Sucrose\ content\ at}{\ }21{\ }\mathrm{DAP}(\%{\ }\mathrm{dry}{\ }\mathrm{wt})}&\\\underline{se1{\ }\mathrm{dose}}&\underline{\mathrm{IL}{\ }451\mathrm{b}}&\underline{\mathrm{IL}{\ }678\mathrm{a}}\\0&9.6&10.3\\1&8.0&10.7\\2&11.3&10.9\\3&15.8&12.2\end{array}\] \end{document} Sucrose content at 21 DAP (typical maturity for harvesting) was observed to increase in the IL451b and IL678a backgrounds from zero to three doses of se1 by 65% and 18% respectively, indicating that this mutation varies in its expression in different genetic backgrounds. Associations between kernel phytoglycogen and starch content and se1 gene dosage are presented. The biochemical lesion associated with the se1 gene product is discussed.

RFLP mapping of the sugary enhancer1 gene in maize

RFLP marker data from an F2∶3 population derived from a cross between a sugary1 (su1) and a sugary enhancer1 (su1, sel) inbred were used to construct a genetic linkage map of maize. This map includes 93 segregating marker loci distributed throughout the maize genome, providing a saturated linkage map that is suitable for linkage analysis with quantitative trait loci (QTL). This population, which has been immortalized in the form of sibbed F2∶3 families, was derived from each of the 214 F2 plants and along with probe data are available to the scientific community. QTL analysis for kernel sucrose (the primary form of sugar) concentration at 20 days after pollination (DAP) uncovered the segregation of seven major QTL influencing sucrose concentration; a locus linked to umc36a described the greatest proportion of the variation (24.7%). Since maltose concentration has previously been reported to be associated with the se1 phenotype, an analysis of probe associations with maltose concentration at 40 DAP was also conducted. The highly significant association of umc36a with maltose and sucrose concentrations provided evidence that this probe is linked to se1. Phenotypic evaluation for the se1 genotype in each F2∶3 family enabled us to map the gene 12.1 cM distal to umc36a. In contrast to previous work where se1 was reported to be located on chromosome four, our data strongly suggest that the sugary enhancer1 locus maps on the the distal portion of the long arm of chromosome 2 in the maize genome.

Partial Resistance of Sugary Enhancer Sweet Corn Genotypes to Two Isolates of the Sugarcane Mosaic Subgroup of Potyviruses

Sweet corn genotypes containing the sugary enhancer (se) allele expressed moderate levels of resistance to maize dwarf mosaic virus (MDMV), a member of the sugarcane mosaic subgroup, under natural infection in the field in Israel. Resistance was identified both in homozygous (sese) and heterozygous (Sese) genotypes. Most (sese) genotypes developed MDMV symptoms when they were mechanically inoculated in the greenhouse. The presence of the virus was verified by ELISA analysis. Plants containing known genes for resistance did not show MDMV symptoms under natural or mechanical inoculation. Two isolates of the sugarcane mosaic virus subgroup of potyviruses, differing in virulence on sweet corn genotypes, were identified. The results show that several se inbred lines contain factors contributing to moderate field resistance to maize potyviruses, but it is not clear whether these factors are pleiotropic or are associated with the se gene. The mechanism of the resistance exhibited in conjunction with the se is not yet understood