Fine mapping of a male sterility gene <Emphasis Type="Italic">ms</Emphasis>-<Emphasis Type="Italic">3</Emphasis> in a novel cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.) mutant

Key message

The cucumber male sterility gene ms - 3 was fine mapped in a 76 kb region harboring an MMD1 -like gene Csa3M006660 that may be responsible for the male sterile in cucumber.

Abstract

A cucumber (Cucumis sativus L.) male sterile mutant (ms-3) in an advanced-generation inbred line was identified, and genetic analysis revealed that the male sterility trait was controlled by a recessive nuclear gene, ms-3, which was stably inherited. Histological studies suggested that the main cause of the male sterility was defective microsporogenesis, resulting in no tetrad or microspores being formed. Bulked segregant analysis (BSA) and genotyping of an F₂ population of 2553 individuals were employed used to fine map ms-3, which was delimited to a 76 Kb region. In this region, a single non-synonymous SNP was found in the Csa3M006660 gene locus, which was predicted to result in an amino acid change. Quantitative RT-PCR analysis of Csa3M006660 was consistent with the fact that it plays a role in the early development of cucumber pollen. The protein encoded by Csa3M006660 is predicted to be homeodomain (PHD) finger protein, and the high degree of sequence conservation with homologs from a range of plant species further suggested the importance of the ms-3 non-synonymous mutation. The data presented here provide support for Csa3M006660 as the most likely candidate gene for Ms-3.

     

Mechanisms of thaxtomin A-induced root toxicity revealed by a thaxtomin A sensitive <Emphasis Type="Italic">Arabidopsis</Emphasis> mutant (<Emphasis Type="Italic">ucu2</Emphasis>-<Emphasis Type="Italic">2/gi</Emphasis>-<Emphasis Type="Italic">2</Emphasis>)

Key message

The Arabidopsis mutant ( ucu2 - 2/gi - 2 ) is thaxtomin A, isoxaben and NPA-sensitive indicated by root growth and ion flux responses providing new insights into these compounds mode of action and interactions.

Abstract

Thaxtomin A (TA) is a cellulose biosynthetic inhibitor (CBI) that promotes plant cell hypertrophy and cell death. Electrophysiological analysis of steady-state K⁺ and Ca²⁺ fluxes in Arabidopsis thaliana roots pretreated with TA for 24 h indicated a disturbance in the regulation of ion movement across the plant cell membrane. The observed inability to control solute movement, recorded in rapidly growing meristematic and elongation root zones, may partly explain typical root toxicity responses to TA treatment. Of note, the TA-sensitive mutant (ucu2-2/gi-2) was more susceptible with K⁺ and Ca²⁺ fluxes altered between 1.3 and eightfold compared to the wild-type control where fluxes altered between 1.2 and threefold. Root growth inhibition assays showed that the ucu2-2/gi-2 mutant had an increased sensitivity to the auxin 2,4-D, but not IAA or NAA; it also had increased sensitivity to the auxin efflux transport inhibitor, 1-naphthylphthalamic acid (NPA), but not 2,3,5- Triiodobenzoic acid (TIBA), when compared to the WT. The NPA sensitivity data were supported by electrophysiological analysis of H⁺ fluxes in the mature (but not elongation) root zone. Increased sensitivity to the CBI, isoxaben (IXB), but not dichlobenil was recorded. Increased sensitivity to both TA and IXB corresponded with higher levels of accumulation of these toxins in the root tissue, compared to the WT. Further root growth inhibition assays showed no altered sensitivity of ucu2-2/gi-2 to two other plant pathogen toxins, alternariol and fusaric acid. Identification of a TA-sensitive Arabidopsis mutant provides further insight into how this CBI toxin interacts with plant cells.

     

Map-based cloning of the dominant genic male sterile <Emphasis Type="Italic">Ms</Emphasis>-<Emphasis Type="Italic">cd1</Emphasis> gene in cabbage (<Emphasis Type="Italic">Brassica oleracea</Emphasis>)

Key message

Using map-based cloning, we delimited the Ms - cd1 gene responsible for the male sterile phenotype in B. oleracea to an approximately 39-kb fragment. Expression analysis suggests that a new predicted gene, a homolog of the Arabidopsis SIED1 gene, is a potential candidate gene.

Abstract

A dominant genic male sterile (DGMS) mutant 79-399-3 in Brassica oleracea (B. oleracea) is controlled by a single gene named Ms-cd1, which was genetically mapped on chromosome C09. The derived DGMS lines of 79-399-3 have been successfully applied in hybrid cabbage breeding and commercial hybrid seed production of several B. oleracea cultivars in China. However, the Ms-cd1 gene responsible for the DGMS has not been identified, and the molecular basis of the DGMS is unclear, which then limits its widespread application in hybrid cabbage seed production. In the present study, a large BC₉ population with 12,269 individuals was developed for map-based cloning of the Ms-cd1 gene, and Ms-cd1 was mapped to a 39.4-kb DNA fragment between two InDel markers, InDel14 and InDel24. Four genes were identified in this region, including two annotated genes based on the available B. oleracea annotation database and two new predicted open reading frames (ORFs). Finally, a newly predicted ORF designated Bol357N3 was identified as the candidate of the Ms-cd1 gene. These results will be useful to reveal the molecular mechanism of the DGMS and develop more practical DGMS lines with stable male sterility for hybrid seed production in cabbage.

     

Drastic anthocyanin increase in response to <Emphasis Type="Italic">PAP1</Emphasis> overexpression in <Emphasis Type="Italic">fls1</Emphasis> knockout mutant confers enhanced osmotic stress tolerance in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Key message

pap1 - D/fls1ko double mutant plants that produce substantial amounts of anthocyanin show tolerance to abiotic stress.

Abstract

Anthocyanins are flavonoids that are abundant in various plants and have beneficial effects on both plants and humans. Many genes in flavonoid biosynthetic pathways have been identified, including those in the MYB-bHLH-WD40 (MBW) complex. The MYB gene Production of Anthocyanin Pigment 1 (PAP1) plays a particularly important role in anthocyanin accumulation. PAP1 expression in many plant systems strongly increases anthocyanin levels, resulting in a dark purple color in many plant organs. In this study, we generated double mutant plants that harbor fls1ko in the pap1-D background (i.e., pap1-D/fls1ko plants), to examine whether anthocyanins can be further enhanced by blocking flavonol biosynthesis under PAP1 overexpression. We also wanted to examine whether the increased anthocyanin levels contribute to defense against osmotic stresses. The pap1-D/fls1ko mutants accumulated higher anthocyanin levels than pap1-D plants in both control and sucrose-treated conditions. However, flavonoid biosynthesis genes were slightly down-regulated in the pap1-D/fls1ko seedlings as compared to their expression in pap1-D seedlings. We also report the performance of pap1-D/fls1ko seedlings in response to plant osmotic stresses.

     

Identification,isolation and expression analysis of eight stress-related <Emphasis Type="Italic">R2R3</Emphasis>-<Emphasis Type="Italic">MYB</Emphasis> genes in tartary buckwheat (<Emphasis Type="Italic">Fagopyrum tataricum</Emphasis>)

Key message

Eight R2R3 - MYB genes in tartary buckwheat were identified, and their expression patterns were comprehensively analyzed, which reveals role in plant response to abiotic stresses.

Abstract

The proteins of the R2R3-MYB superfamily play key roles in the growth and development processes as well as defense responses in plants. However, their characteristics and functions have not been fully investigated in tartary buckwheat (Fagopyrum tataricum), a strongly abiotic resistant coarse cereal. In this article, eight tartary buckwheat R2R3-MYB genes were isolated with full-length cDNA and DNA sequences. Phylogenetic analysis of the members of the R2R3-MYB superfamily between Arabidopsis and tartary buckwheat revealed that the assumed functions of the eight tartary buckwheat R2R3-MYB proteins are divided into five Arabidopsis functional subgroups that are involved in abiotic stress. Expression analysis during abiotic stress and exogenous phytohormone treatments identified that the eight R2R3-MYB genes responded to one or more treatments. This study is the first comprehensive analysis of the R2R3-MYB gene family in tartary buckwheat under abiotic stress.

     

<Emphasis Type="Italic">PAD4</Emphasis>, <Emphasis Type="Italic">LSD1</Emphasis> and <Emphasis Type="Italic">EDS1</Emphasis> regulate drought tolerance,plant biomass production,and cell wall properties

Key message

Arabidopsis and poplar with modified PAD4, LSD1 and EDS1 genes exhibit successful growth under drought stress. The acclimatory strategies depend on cell division/cell death control and altered cell wall composition.

Abstract

The increase of plant tolerance towards environmental stresses would open much opportunity for successful plant cultivation in these areas that were previously considered as ineligible, e.g. in areas with poor irrigation. In this study, we performed functional analysis of proteins encoded by PHYTOALEXIN DEFICIENT 4 (PAD4), LESION SIMULATING DISEASE 1 (LSD1) and ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) genes to explain their role in drought tolerance and biomass production in two different species: Arabidopsis thaliana and Populus tremula × tremuloides. Arabidopsis mutants pad4-5, lsd1-1, eds1-1 and transgenic poplar lines PAD4-RNAi, LSD1-RNAi and ESD1-RNAi were examined in terms of different morphological and physiological parameters. Our experiments proved that Arabidopsis PAD4, LSD1 and EDS1 play an important role in survival under drought stress and regulate plant vegetative and generative growth. Biomass production and acclimatory strategies in poplar were also orchestrated via a genetic system of PAD4 and LSD1 which balanced the cell division and cell death processes. Furthermore, improved rate of cell division/cell differentiation and altered physical properties of poplar wood were the outcome of PAD4- and LSD1-dependent changes in cell wall structure and composition. Our results demonstrate that PAD4, LSD1 and EDS1 constitute a molecular hub, which integrates plant responses to water stress, vegetative biomass production and generative development. The applicable goal of our research was to generate transgenic plants with regulatory mechanism that perceives stress signals to optimize plant growth and biomass production in semi-stress field conditions.

     

The seed dormancy allele <Emphasis Type="Italic">TaSdr</Emphasis>-<Emphasis Type="Italic">A1a</Emphasis> associated with pre-harvest sprouting tolerance is mainly present in Chinese wheat landraces

Key message

We cloned TaSdr - A1 gene, and developed a gene-specific marker for TaSdr - A1 . A QTL for germination index at the TaSdr - A1 locus was identified in the Yangxiaomai/Zhongyou 9507 RIL population.

Abstract

Pre-harvest sprouting (PHS) affects yield and end-use quality in bread wheat (Triticum aestivum L.). In the present study we found an association between the TaSdr-A1 gene and PHS tolerance in bread wheat. TaSdr-A1 on chromosome 2A was cloned using a homologous cloning approach. Sequence analysis of TaSdr-A1 revealed an SNP at position 643, with the G allele being present in genotypes with lower germination index (GI) values and A in those with higher GI. These alleles were designated as TaSdr-A1a and TaSdr-A1b, respectively. A cleaved amplified polymorphism sequence (CAPS) marker Sdr2A based on the SNP was developed, and linkage mapping and QTL analysis were conducted to confirm the association between TaSdr-A1 and seed dormancy. Sdr2A was located in a 2.9 cM interval between SSR markers Xgwm95 and Xgwm372. A QTL for GI at the TaSdr-A1 locus explained 6.6, 7.3, and 8.2 % of the phenotypic variances in a Yangxiaomai/Zhongyou 9507 RIL population grown at Beijing, Shijiazhuang, and the averaged data from the two environments, respectively. Two sets of Chinese wheat cultivars used for validating the TaSdr-A1 polymorphism and the corresponding gene-specific marker Sdr2A showed that TaSdr-A1 was significantly associated with GI. Among 29 accessions with TaSdr-A1a, 24 (82.8 %) were landraces, indicating the importance of Chinese wheat landraces as sources of PHS tolerance. This study identified a novel PHS resistance allele TaSdr-A1a mainly presented in Chinese landraces and it is likely to be the causal gene for QPhs.ccsu-2A.3, providing new information for an understanding of seed dormancy.

     

Glutathione homeostasis and Cd tolerance in the <Emphasis Type="Italic">Arabidopsis</Emphasis><Emphasis Type="Italic">sultr1;1</Emphasis>-<Emphasis Type="Italic">sultr1;2</Emphasis> double mutant with limiting sulfate supply

Key message

Cadmium sensitivity in sultr1;1 - sultr1;2 double mutant with limiting sulfate supply is attributed to the decreased glutathione content that affected oxidative defense but not phytochelatins’ synthesis.

Abstract

In plants, glutathione (GSH) homeostasis plays pivotal role in cadmium (Cd) detoxification. GSH is synthesized by sulfur (S) assimilation pathway. Many studies have tried to investigate the role of GSH homeostasis on Cd tolerance using mutants; however, most of them have focused on the last few steps of S assimilation. Until now, mutant evidence that explored the relationship between GSH homeostasis on Cd tolerance and S absorption is rare. To further reveal the role of GSH homeostasis on Cd stress, the wild-type and a sultr1;1-sultr1;2 double mutant which had a defect in two distinct high-affinity sulfate transporters were used in this study. Growth parameters, biochemical or zymological indexes and S assimilation-related genes’ expression were compared between the mutant and wild-type Arabidopsis plants. It was found that the mutations of SULTR1;1 and SULTR1;2 did not affect Cd accumulation. Compared to the wild-type, the double mutant was more sensitive to Cd under limited sulfate supply and suffered from stronger oxidative damage. More importantly, under the same condition, lower capacity of S assimilation resulted in decreased GSH content in mutant. Faced to the limited GSH accumulation, mutant seedlings consumed a large majority of GSH in pool for the synthesis of phytochelatins rather than participating in the antioxidative defense. Therefore, homeostasis of GSH, imbalance between antioxidative defense and severe oxidative damage led to hypersensitivity of double mutant to Cd under limited sulfate supply.

     

Identification and fine mapping of a stay-green gene (<Emphasis Type="Italic">Brnye1</Emphasis>) in pakchoi (<Emphasis Type="Italic">Brassica campestris</Emphasis> L. ssp. <Emphasis Type="Italic">chinensis</Emphasis>)

Key message

Using bulked segregant analysis combined with next-generation sequencing, we delimited the Brnye1 gene responsible for the stay-green trait of nye in pakchoi. Sequence analysis identified Bra019346 as the candidate gene.

Abstract

“Stay-green” refers to a plant trait whereby leaves remain green during senescence. This trait is useful in the cultivation of pakchoi (Brassica campestris L. ssp. chinensis), which is marketed as a green leaf product. This study aimed to identify the gene responsible for the stay-green trait in pakchoi. We identified a stay-green mutant in pakchoi, which we termed “nye”. Genetic analysis revealed that the stay-green trait is controlled by a single recessive gene, Brnye1. Using the BSA-seq method, a 3.0-Mb candidate region was mapped on chromosome A03, which helped us localize Brnye1 to an 81.01-kb interval between SSR markers SSRWN27 and SSRWN30 via linkage analysis in an F₂ population. We identified 12 genes in this region, 11 of which were annotated based on the Brassica rapa annotation database, and one was a functionally unknown gene. An orthologous gene of the Arabidopsis gene AtNYE1, Bra019346, was identified as the potential candidate for Brnye1. Sequence analysis revealed a 40-bp insertion in the second exon of Bra019346 in nye, which generated the TAA stop codon. A candidate gene-specific Indel marker in 1561 F₂ individuals showed perfect cosegregation with Brnye1 in the nye mutant. These results provide a foundation for uncovering the molecular mechanism of the stay-green trait in pakchoi.

     

Characterisation of a novel quantitative trait locus, <Emphasis Type="Italic">GN4</Emphasis>-<Emphasis Type="Italic">1</Emphasis>, for grain number and yield in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Key message

A novel QTL for grain number, GN4-1, was identified and fine-mapped to an ~ 190-kb region on the long arm of rice chromosome 4.

Abstract

Rice grain yield is primarily determined by three components: number of panicles per plant, grain number per panicle and grain weight. Among these traits, grain number per panicle is the major contributor to grain yield formation and is a crucial trait for yield improvement. In this study, we identified a major quantitative trait locus (QTL) responsible for rice grain number on chromosome 4, designated GN4-1 (a QTL for Grain Number on chromosome 4), using advanced segregating populations derived from the crosses between an elite indica cultivar ‘Zhonghui 8006’ (ZH8006) and a japonica rice ‘Wuyunjing 8’ (WYJ8). GN4-1 was delimited to an ~ 190-kb region on chromosome 4. The genetic effect of GN4-1 was estimated using a pair of near-isogenic lines. The GN4-1 gene from WYJ8 promoted accumulation of cytokinins in the inflorescence and increased grain number per panicle by ~ 17%. More importantly, introduction of the WYJ8 GN4-1 gene into ZH8006 increased grain yield by ~ 14.3 and ~ 11.5% in the experimental plots in 2014 and 2015, respectively. In addition, GN4-1 promoted thickening of the culm and may enhance resistance to lodging. These results demonstrate that GN4-1 is a potentially valuable gene for improvement of yield and lodging resistance in rice breeding.

     

Update on <Emphasis Type="Italic">transparent testa</Emphasis> mutants from <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>: characterisation of new alleles from an isogenic collection

Main conclusion

We present a comprehensive overview on flavonoid-related phenotypes of A. thaliana tt and tds mutants, provide tools for their characterisation, increase the number of available alleles and demonstrate that tds3 is allelic to tt12 and tds5 to aha10.Flavonoid biosynthesis is one of the best-studied secondary metabolite pathways in plants. In the model system Arabidopsis thaliana it leads to the synthesis of three phenolic compound classes: flavonol glycosides, anthocyanins and proanthocyanidins (PAs). PAs appear brown in their oxidised polymeric forms, and most A. thaliana mutants impaired in flavonoid accumulation were identified through screens for lack of this seed coat pigmentation. These mutants are referred to as transparent testa (tt) or tannin-deficient seed (tds). More than 20 mutants of these types have been published, probably representing most of the genes relevant for PA accumulation in A. thaliana. However, data about the genes involved in PA deposition or oxidation are still rather scarce. Also, for some of the known mutants it is unclear if they represent additional loci or if they are allelic to known genes. For the present study, we have performed a systematic phenotypic characterisation of almost all available tt and tds mutants and built a collection of mutants in the genetic background of the accession Columbia to minimise effects arising from ecotype variation. We have identified a novel tt6 allele from a forward genetic screen and demonstrated that tds3 is allelic to tt12 and tds5 to aha10.

     

Constitutive expression of the <Emphasis Type="Italic">tzs</Emphasis> gene from <Emphasis Type="Italic">Agrobacterium tumefaciens virG</Emphasis> mutant strains is responsible for improved transgenic plant regeneration in cotton meristem transformation

Key message

virG mutant strains of a nopaline type of Agrobacterium tumefaciens increase the transformation frequency in cotton meristem transformation. Constitutive cytokinin expression from the tzs gene in the virG mutant strains is responsible for the improvement.

Abstract

Strains of Agrobacterium tumefaciens were tested for their ability to improve cotton meristem transformation frequency. Two disarmed A. tumefaciens nopaline strains with either a virGN54D constitutively active mutation or virGI77V hypersensitive induction mutation significantly increased the transformation frequency in a cotton meristem transformation system. The virG mutant strains resulted in greener explants after three days of co-culture in the presence of light, which could be attributed to a cytokinin effect of the mutants. A tzs knockout strain of virGI77V mutant showed more elongated, less green explants and decreased cotton transformation frequency, as compared to a wild type parental strain, suggesting that expression of the tzs gene is required for transformation frequency improvement in cotton meristem transformation. In vitro cytokinin levels in culture media were tenfold higher in the virGN54D strain, and approximately 30-fold higher in the virGI77V strain, in the absence of acetosyringone induction, compared to the wild type strain. The cytokinin level in the virGN54D strain is further increased upon acetosyringone induction, while the cytokinin level in the virGI77V mutant is decreased by induction, suggesting that different tzs gene expression regulation mechanisms are present in the two virG mutant strains. Based on these data, we suggest that the increased cytokinin levels play a major role in increasing Agrobacterium attachment and stimulating localized division of the attached plant cells.

     

Epigenetic regulation of <Emphasis Type="Italic">MdMYB1</Emphasis> is associated with paper bagging-induced red pigmentation of apples

Main conclusion

Paper-bagging treatment can transform non-transcribed MdMYB1 - 2 and MdMYB1 - 3 alleles into transcribed alleles through epigenetic regulations, resulting in the red pigmentation of a normally non-red apple cultivar ‘Mutsu.’ Anthocyanin biosynthesis in apples is regulated by MdMYB1/A/10, an R2R3-Type MYB gene. ‘Mutsu,’ a triploid apple cultivar harboring non-transcribed MdMYB1-2 and MdMYB1-3 alleles, retains green skin color under field conditions. However, it can show red/pink pigmentation under natural or artificial ultraviolet-B (UV-B) light exposure after paper-bagging and bag removal treatment. In the present study, we found that in ‘Mutsu,’ paper bagging-induced red pigmentation was due to the activation of non-transcribed MdMYB1-2/-3 alleles, which triggered the expression of downstream anthocyanin biosynthesis genes in a UV-B-dependent manner. By monitoring the epigenetic changes during UV-B-induced pigmentation, no significant differences in DNA methylation and histone modifications in the 5′ upstream region of MdMYB1-2/-3 were recorded between the UV-B-treated fruit skin (red) and the fruit skin treated only by white light (green). In contrast, bag treatment lowered the DNA methylation in this region of MdMYB1-2/-3 alleles. Similarly, higher levels of histone H3 acetylation and trimethylation of H3 tail at lysine 4, and lower level of trimethylation of H3 tail at lysine 27 were observed in the 5′ upstream region of MdMYB1-2/-3 in the skin of the fruit immediately after bag removal. These results suggest that bagging treatment can induce epigenetic changes, facilitating the binding of trans factor(s) to MdMYB1-2/-3 alleles, resulting in the activation of these MYBs after bag removal.

     

Brassinosteroid (BR) biosynthetic gene <Emphasis Type="Italic">lhdd10</Emphasis> controls late heading and plant height in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Key message

A Brd2 allele suppresses heading date by altering the expression of heading date regulators such as OsMADS50 , and also negatively regulates chlorophyll biosynthesis.

Abstract

Heading date and plant height are important determinants of yield in rice (Oryza sativa L.). In this study, we characterized a late heading, dwarf mutant known as lhdd10 selected following ethyl methane sulfonate (EMS)-treatment of ssp. indica cultivar 93-11. lhdd10 showed late heading, dwarfness and slightly darker-green leaves than wild-type 93-11 under long-day and short-day conditions. We isolated lhdd10 by map-based cloning; it encoded a putative FAD-linked oxidoreductase protein (a brassinosteroid biosynthetic gene) that localized to the nucleus. LHDD10 was constitutively expressed in various tissues, but more so in shoot apices and panicles. Our data showed that lhdd10 influences heading date by controlling the expression of heading date regulators, such as OsMADS50 in both LD and SD conditions. lhdd10 also negatively regulated expression of chlorophyll biosynthetic genes to reduce the chlorophyll content. Our data indicated that BRs play important roles in regulating heading date and chlorophyll biosynthesis. This work provides material that will allow study of how BRs regulate heading date in rice.

     

Fine-mapping and identification of a novel locus <Emphasis Type="Italic">Rsc15</Emphasis> underlying soybean resistance to <Emphasis Type="Italic">Soybean mosaic virus</Emphasis>

Key message

Rsc15, a novel locus underlying soybean resistance to SMV, was fine mapped to a 95-kb region on chromosome 6. The Rsc15- mediated resistance is likely attributed to the gene GmPEX14 , the relative expression of which was highly correlated with the accumulation of H ₂ O ₂ along with the activities of POD and CAT during the early stages of SMV infection in RN-9.

Abstract

Soybean mosaic virus (SMV) causes severe yield losses and seed quality deterioration in soybean [Glycine max (L.) Merr.] worldwide. A series of single dominant SMV resistance genes have been identified on respective soybean chromosomes 2, 13 and 14, while one novel locus, Rsc15, underlying resistance to the virulent SMV strain SC15 from soybean cultivar RN-9 has been recently mapped to a 14.6-cM region on chromosome 6. However, candidate gene has not yet been identified within this region. In the present study, we aimed to fine map the Rsc15 region and identify candidate gene(s) for this invaluable locus. High-resolution fine-mapping revealed that the Rsc15 gene was located in a 95-kb genomic region which was flanked by the two simple sequence repeat (SSR) markers SSR_06_17 and BARCSOYSSR_06_0835. Allelic sequence comparison and expression profile analysis of candidate genes inferred that the gene Glyma.06g182600 (designated as GmPEX14) was the best candidate gene attributing for the resistance of Rsc15, and that genes encoding receptor-like kinase (RLK) (i.e., Glyma.06g175100 and Glyma.06g184400) and serine/threonine kinase (STK) (i.e., Glyma.06g182900 and Glyma.06g183500) were also potential candidates. High correlations were established between the relative expression level of GmPEX14 and the hydrogen peroxide (H₂O₂) concentration and activities of catalase (CAT) and peroxidase (POD) during the early stages of SMV-SC15 infection in RN-9. The results of the present study will be useful in marker-assisted breeding for SMV resistance and will lead to further understanding of the molecular mechanisms of host resistance against SMV.

     

Revision of the <Emphasis Type="Italic">Rhynchospora glomerata</Emphasis> species complex,focusing on the taxonomic status of <Emphasis Type="Italic">R. leptocarpa</Emphasis> (Cyperaceae)

Rhynchospora glomerata and its closest relatives comprise a group of beakesedges widespread and frequent in much of North America. The classification of the R. glomerata complex remains unresolved and controversial. The goals of this study are to determine the number of taxa in the complex and their ranks, and identify their best diagnostic characters. Measurements of eight characters from each of 101 specimens from throughout the geographic range of the complex furnished data for morphometric analyses. These analyses reveal the R. glomerata complex contains three species and no infraspecific taxa: R. capitellata, R. glomerata, and R. leptocarpa. We detected 10 validly published basionyms in the complex, five of which required lectotypification. Accordingly, we designated lectotypes for R. glomerata var. discutiens, R. glomerata var. minor, R. glomerata var. paniculata, and R. glomerata var. robustior, and the second-step lectotype for R. capitellata var. controversa.