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.

     

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.

     

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.

     

<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.

     

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.

     

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.

     

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.

     

Tight repulsion linkage between <Emphasis Type="Italic">Sr36</Emphasis> and <Emphasis Type="Italic">Sr39</Emphasis> was revealed by genetic,cytogenetic and molecular analyses

Key message

The shortening of Aegilops speltoides segment did not facilitate recombination between stem rust resistance genes Sr36 and Sr39 . Robustness of marker rwgs28 for marker-assisted selection of Sr39 was demonstrated.

Abstract

Stem rust resistance genes Sr39 and Sr36 were transferred from Aegilops speltoides and Triticum timopheevii, respectively, to chromosome 2B of wheat. Genetic stocks RL6082 and RWG1 carrying Sr39 on a large and a shortened Ae. speltoides segments, respectively, and the Sr36-carrying Australian wheat cultivar Cook were used in this study. This investigation was planned to determine the genetic relationship between these genes. Stem rust tests on F₃ populations derived from RL6082/Cook and RWG1/Cook crosses showed tight repulsion linkage between Sr39 and Sr36. The genomic in situ hybridization analysis of heterozygous F₃ family from the RWG1/Cook population showed that the translocated segments do not overlap. Meiotic analysis on the F₁ plant from RWG1/Cook showed two univalents at the metaphase and anaphase stages in a majority of the cells indicating absence of pairing. Since meiotic pairing has been reported to initiate at the telomere, pairing and recombination may be inhibited due to very little wheat chromatin in the distal end of the chromosome arm 2BS in RWG1. The Sr39-carrying large Ae. speltoides segment transmitted preferentially in the RL6082/Cook F₃ population, whereas the Sr36-carrying T. timopheevii segment over-transmitted in the RWG1/Cook cross. Genotyping with the co-dominant Sr39- and Sr36-linked markers rwgs28 and stm773-2, respectively, matched the phenotypic classification of F₃ families. The RWG1 allele amplified by rwgs28 was diagnostic for the shortened Ae. speltoides segment and alternate alleles were amplified in 29 Australian cultivars. Marker rwgs28 will be useful in marker-assisted pyramiding of Sr39 with other genes.

     

Cytogenetic mapping of a major locus for resistance to Fusarium head blight and crown rot of wheat on <Emphasis Type="Italic">Thinopyrum elongatum</Emphasis> 7EL and its pyramiding with valuable genes from a <Emphasis Type="Italic">Th. ponticum</Emphasis> homoeologous arm onto bread wheat 7DL

Key message

A major locus for resistance to different Fusarium diseases was mapped to the most distal end of Th. elongatum 7EL and pyramided with Th. ponticum beneficial genes onto wheat 7DL.

Abstract

Perennial Triticeae species of the Thinopyrum genus are among the richest sources of valuable genes/QTL for wheat improvement. One notable and yet unexploited attribute is the exceptionally effective resistance to a major wheat disease worldwide, Fusarium head blight, associated with the long arm of Thinopyrum elongatum chromosome 7E (7EL). We targeted the transfer of the temporarily designated Fhb-7EL locus into bread wheat, pyramiding it with a Th. ponticum 7el₁L segment stably inserted into the 7DL arm of wheat line T4. Desirable genes/QTL mapped along the T4 7el₁L segment determine resistance to wheat rusts (Lr19, Sr25) and enhancement of yield-related traits. Mapping of the Fhb-7EL QTL, prerequisite for successful pyramiding, was established here on the basis of a bioassay with Fusarium graminearum of different 7EL-7el₁L bread wheat recombinant lines. These were obtained without resorting to any genetic pairing promotion, but relying on the close 7EL-7el₁L homoeology, resulting in 20% pairing frequency between the two arms. Fhb-7EL resided in the telomeric portion and resistant recombinants could be isolated with useful combinations of more proximally located 7el₁L genes/QTL. The transferred Fhb-7EL locus was shown to reduce disease severity and fungal biomass in grains of infected recombinants by over 95%. The same Fhb-7EL was, for the first time, proved to be effective also against F. culmorum and F. pseudograminearum, predominant agents of crown rot. Prebreeding lines possessing a suitable 7EL-7el₁L gene/QTL assembly showed very promising yield performance in preliminary field tests.

     

Fine mapping of QTL <Emphasis Type="Italic">qCTB10</Emphasis>-<Emphasis Type="Italic">2</Emphasis> that confers cold tolerance at the booting stage in rice

Key message

The QTL qCTB10 - 2 controlling cold tolerance at the booting stage in rice was delimited to a 132.5 kb region containing 17 candidate genes and 4 genes were cold-inducible.

Abstract

Low temperature at the booting stage is a major abiotic stress-limiting rice production. Although some QTL for cold tolerance in rice have been reported, fine mapping of those QTL effective at the booting stage is few. Here, the near-isogenic line ZL31-2, selected from a BC₇F₂ population derived from a cross between cold-tolerant variety Kunmingxiaobaigu (KMXBG) and the cold-sensitive variety Towada, was used to map a QTL on chromosome 10 for cold tolerance at the booting stage. Using BC₇F₃ and BC₇F₄ populations, we firstly confirmed qCTB10-2 and gained confidence that it could be fine mapped. QTL qCTB10-2 explained 13.9 and 15.9% of the phenotypic variances in those two generations, respectively. Using homozygous recombinants screened from larger BC₇F₄ and BC₇F₅ populations, qCTB10-2 was delimited to a 132.5 kb region between markers RM25121 and MM0568. 17 putative predicted genes were located in the region and only 5 were predicted to encode expressed proteins. Expression patterns of these five genes demonstrated that, except for constant expression of LOC_Os10g11820, LOC_Os10g11730, LOC_Os10g11770, and LOC_Os10g11810 were highly induced by cold stress in ZL31-2 compared to Towada, while LOC_Os10g11750 showed little difference. Our results provide a basis for identifying the genes underlying qCTB10-2 and indicate that markers linked to the qCTB10-2 locus can be used to improve the cold tolerance of rice at the booting stage by marker-assisted selection.

     

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.

     

<Emphasis Type="Italic">qRfg3</Emphasis>, a novel quantitative resistance locus against <Emphasis Type="Italic">Gibberella</Emphasis> stalk rot in maize

Key message

A quantitative trait locus  qRfg3 imparts recessive resistance to maize Gibberella stalk rot. qRfg3 has been mapped into a 350-kb interval and could reduce the disease severity index by ~26.6%.

Abstract

Gibberella stalk rot, caused by the fungal pathogen Fusarium graminearum, severely affects maize yield and grain quality worldwide. To identify more resistance quantitative trait loci (QTLs) against this disease, we analyzed a recombinant inbred line (RIL) population derived from a cross between resistant H127R and susceptible C7-2 inbred lines. Within this population, maize resistance to Gibberella stalk rot had high broad-sense heritability. A major QTL, qRfg3, on chromosome 3 was consistently detected across three field trials, accounting for 10.7–19.4% of the total phenotypic variation. Using a progeny-based sequential fine-mapping strategy, we narrowed qRfg3 down to an interval of ~350 kb. We further demonstrated that qRfg3 is a recessive resistance locus to Gibberella stalk rot that reduced the disease severity index by ~26.6%. Both the gene location and recessive genetic mode distinguish qRfg3 from other stalk rot resistance loci. Hence, qRfg3 is valuable as a complement to existing resistance QTLs to improve maize resistance to Gibberella stalk rot.

     

A mutant in the <Emphasis Type="Italic">CsDET2</Emphasis> gene leads to a systemic brassinosteriod deficiency and <Emphasis Type="Italic">super compact </Emphasis>phenotype in cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.)

Key message

A novel dwarf cucumber mutant, scp-2, displays a typical BR biosynthesis-deficient phenotype, which is due to a mutation in CsDET2 for a steroid 5-alpha-reductase.

Abstract

Brassinosteroids (BRs) are a group of plant hormones that play important roles in the development of plant architecture, and extreme dwarfism is a typical outcome of BR-deficiency. Most cucumber (Cucumis sativus L.) varieties have an indeterminate growth habit, and dwarfism may have its value in manipulation of plant architecture and improve production in certain production systems. In this study, we identified a spontaneous dwarf mutant, super compact-2 (scp-2), that also has dark green, wrinkle leaves. Genetic analyses indicated that scp-2 was different from two previously reported dwarf mutants: compact (cp) and super compact-1 (scp-1). Map-based cloning revealed that the mutant phenotype was due to two single nucleotide polymorphism and a single-base insertion in the CsDET2 gene that resulted in a missense mutation in a conserved amino acid and thus a truncated protein lacking the conserved catalytic domains in the predicted steroid 5α-reductase protein. Measurement of endogenous hormone levels indicated a reduced level of brassinolide (BL, a bioactive BR) in scp-2, and the mutant phenotype could be partially rescued by the application of epibrassinolide (EBR). In addition, scp-2 mutant seedlings exhibited dark-grown de-etiolation, and defects in cell elongation and vascular development. These data support that scp-2 is a BR biosynthesis-deficient mutant, and that the CsDET2 gene plays a key role in BR biosynthesis in cucumber. We also described the systemic BR responses and discussed the specific BR-related phenotypes in cucumber plants.

     

Low molecular weight glutenin subunit gene composition at <Emphasis Type="Italic">Glu</Emphasis>-<Emphasis Type="Italic">D3</Emphasis> loci of <Emphasis Type="Italic">Aegilops tauschii</Emphasis> and common wheat and a further view of wheat evolution

Key message

A comprehensive comparison of LMW-GS genes between Ae. tauschii and its progeny common wheat.

Abstract

Low molecular weight glutenin subunits (LMW-GSs) are determinant of wheat flour processing quality. However, the LMW-GS gene composition in Aegilops tauschii, the wheat D genome progenitor, has not been comprehensively elucidated and the impact of allohexaploidization on the Glu-D3 locus remains elusive. In this work, using the LMW-GS gene molecular marker system and the full-length gene-cloning method, LMW-GS genes at the Glu-D3 loci of 218 Ae. tauschii and 173 common wheat (Triticum aestivum L.) were characterized. Each Ae. tauschii contained 11 LMW-GS genes, and the whole collection was divided into 25 haplotypes (AeH01–AeH25). The Glu-D3 locus in common wheat lacked the LMW-GS genes D3-417, D3-507 and D3-552, but shared eight genes of identical open reading frame (ORF) sequences when compared to that of Ae. tauschii. Therefore, the allohexaploidization induces deletions, but exerts no influence on LMW-GS gene coding sequences at the Glu-D3 locus. 92.17% Ae. tauschii had 7-9 LMW-GSs, more than the six subunits in common wheat. The haplotypes AeH16, AeH20 and AeH23 of Ae. tauschii ssp. strangulate distributed in southeastern Caspian Iran were the main putative D genome donor of common wheat. These results facilitate the utilization of the Ae. tauschii glutenin gene resources and the understanding of wheat evolution.

     

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.     

Molecular insights into the origin of the brown rust resistance gene <Emphasis Type="Italic">Bru</Emphasis>1 among <Emphasis Type="Italic">Saccharum</Emphasis> species

Key message

Analysis of 387 sugarcane clones using Bru 1 diagnostic markers revealed two possible sources of Bru 1 in Chinese cultivars: one from Saccharum spontaneum and another from Saccharum robustum of New Guinea.

Abstract

Sugarcane brown rust (SBR) is an important fungal disease in many sugarcane production areas around the world, and can cause considerable yield losses in susceptible sugarcane cultivars. One major SBR resistance gene, named Bru1, initially identified from cultivar R570, was shown to be a major SBR resistance source in most of the sugarcane producing areas of the world. In this study, by using the two Bru1-associated markers, R12H16 and 9O20-F4, we surveyed the presence of Bru1 in a Chinese sugarcane germplasm collection of 387 clones, consisting of 228 hybrid cultivars bred by different Chinese sugarcane breeding establishments, 54 exotic hybrid cultivars introduced from other countries and 105 clones of sugarcane ancestral species. The Bru1-bearing haplotype was detected in 43.4% of Chinese sugarcane cultivars, 20.4% of exotic hybrid cultivars, and only 3.8% of ancestral species. Among the 33 Chinese cultivars for which phenotypes of resistance to SBR were available, Bru1 was present in 69.2% (18/26) of the resistant clones. Analyses of the allelic sequence variations of R12H16 and 9O20-F4 suggested two possible sources of Bru1 in Chinese cultivars: one from S. spontaneum and another from S. robustum of New Guinea. In addition, we developed an improved Bru1 diagnostic marker, 9O20-F4-HaeIII, which can eliminate all the false results of 9O20-F4-RsaI observed among S. spontaneum, as well as a new dominant Bru1 diagnostic marker, R12E03-2, from the BAC ShCIR12E03. Our results provide valuable information for further efforts of breeding SBR-resistant varieties, searching new SBR resistance sources and cloning of Bru1 in sugarcane.

     

Loci on chromosomes 1A and 2A affect resistance to tan (yellow) spot in wheat populations not segregating for <Emphasis Type="Italic">tsn1</Emphasis>

Key message

QTL for tan spot resistance were mapped on wheat chromosomes 1A and 2A. Lines were developed with resistance alleles at these loci and at the tsn1 locus on chromosome 5B. These lines expressed significantly higher resistance than the parent with tsn1 only.

Abstract

Tan spot (syn. yellow spot and yellow leaf spot) caused by Pyrenophora tritici-repentis is an important foliar disease of wheat in Australia. Few resistance genes have been mapped in Australian germplasm and only one, known as tsn1 located on chromosome 5B, is known in Australian breeding programs. This gene confers insensitivity to the fungal effector ToxA. The main aim of this study was to map novel resistance loci in two populations: Calingiri/Wyalkatchem, which is fixed for the ToxA-insensitivity allele tsn1, and IGW2574/Annuello, which is fixed for the ToxA-sensitivity allele Tsn1. A second aim was to combine new loci with tsn1 to develop lines with improved resistance. Tan spot severity was evaluated at various growth stages and in multiple environments. Symptom severity traits exhibited quantitative variation. The most significant quantitative trait loci (QTL) were detected on chromosomes 2A and 1A. The QTL on 2A explained up to 29.2% of the genotypic variation in the Calingiri/Wyalkatchem population with the resistance allele contributed by Wyalkatchem. The QTL on 1A explained up to 28.1% of the genotypic variation in the IGW2574/Annuello population with the resistance allele contributed by Annuello. The resistance alleles at both QTL were successfully combined with tsn1 to develop lines that express significantly better resistance at both seedling and adult plant stages than Calingiri which has tsn1 only.