Development of marker-free and transgene insertion site-defined (MFTID) transgenic plants is essential for safe application of transgenic crops. However, MFTID plants have not been reported for wheat (Triticum aestivum). Here, we prepared a RNAi cassette for suppressing lipoxygenase (LOX) gene expression in wheat grains using a double right border T-DNA vector. The resultant construct was introduced into wheat genome via Agrobacterium-mediated transformation, with four homozygous marker-free transgenic lines (namely GLRW-1, -3, -5 and -8) developed. Aided by the newly published wheat genome sequence, the T-DNA insertion sites in GLRW-3 and GLRW-8 were elucidated at base-pair resolution. While the T-DNA in GLRW-3 inserted in an intergenic region, that of GLRW-8 inactivated an endogenous gene, which was thus excluded from further analysis. Compared to wild -type (WT) control, GLRW-1, -3 and -5 showed decreased LOX gene expression, lower LOX activity and less lipid peroxidation in the grains; they also exhibited significantly higher germination rates and better seedling growth after artificial ageing treatment. Interestingly, the three GLRW lines also had substantially increased contents of several fatty acids (e.g., linoleic acid and linolenic acid) in their grain and flour samples than WT control. Collectively, our data suggest that suppression of grain LOX activity can be employed to improve the storability and fatty acid content of wheat seeds and that the MFTID line GLRW-3 is likely of commercial value. Our approach may also be useful for developing the MFTID transgenic lines of other crops with enhanced grain storability and fatty acid content.

Grain yield in cereal crops is a complex trait controlled by multiple genes and influenced by developmental processes and environment. Here we report the effects of alleles Rht8 and Ppd-D1a on plant height, time to heading, and grain yield and its component traits. Association analysis and quantitative trait locus mapping using phenotypic data from 15 environments led to the following conclusions. First, both Rht8 and Ppd-D1a reduce plant height. However, Ppd-D1a but not Rht8 causes earlier heading. Second, both Rht8 and Ppd-D1a promote grain yield and affect component traits. Their combined effects are substantially larger than those conferred by either allele alone. Third, promotion of grain yield by Rht8 and Ppd-D1a is through increasing fertile spikelet number. We speculate that Rht8 and Ppd-D1a act independently and additively in control of plant height, grain yield and yield component. Combination of the two alleles is desirable for adjusting plant height and enhancing grain yield and abiotic stress tolerance.

氨基酸是蛋白质的基本组成单位,是人体必需的重要营养物质.彩色小麦被认为是一类新型的营养保健小麦品种,但对其籽粒中氨基酸含量的研究很少.本研究首次利用高效液相色谱法比较分析了种植于3个环境中的彩色小麦近等基因系(蓝粒小麦‘科兴611’,紫粒小麦‘科兴617’和白粒小麦轮回亲本‘济麦22’)籽粒中多种氨基酸的含量.结果 表明:蓝粒小麦‘科兴611’的必需氨基酸含量、非必需氨基酸含量及总氨基酸含量均显著地高于紫粒小麦‘科兴617’和白粒亲本‘济麦22’.紫粒小麦‘科兴617’和白粒小麦‘济麦22’相比,必需氨基酸含量、非必需氨基酸含量及总氨基酸含量相近,甚至低于‘济麦22’.因此,蓝粒小麦籽粒氨基酸含量高,有益于满足人类营养需求,同时可作为育种材料改良小麦品种的氨基酸含量,尤其是提高限制性氨基酸的含量,进而提高小麦的营养品质.

Powdery mildew disease, elicited by the obligate fungal pathogen Blumeria graminis f.sp. tritici (Bgt), causes widespread yield losses in global wheat crop. However, the molecular mechanisms governing wheat defense to Bgt are still not well understood. Here we found that TuACO3, encoding the 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase functioning in ethylene (ET) biosynthesis, was induced by Bgt infection of the einkorn wheat Triticum urartu, which was accompanied by increased ET content. Silencing TuACO3 decreased ET production and compromised wheat defense to Bgt, whereas both processes were enhanced in the transgenic wheat overexpressing TuACO3. TuMYB46L, phylogenetically related to Arabidopsis MYB transcription factor AtMYB46, was found to bind to the TuACO3 promoter region in yeast-one-hybrid and EMSA experiments. TuMYB46L expression decreased rapidly following Bgt infection. Silencing TuMYB46L promoted ET content and Bgt defense, but the reverse was observed when TuMYB46L was overexpressed. Hence, decreased expression of TuMYB46L permits elevated function of TuACO3 in ET biosynthesis in Bgt-infected wheat. The TuMYB46L-TuACO3 module regulates ET biosynthesis to promote einkorn wheat defense against Bgt. Furthermore, we found four chitinase genes acting downstream of the TuMYB46L-TuACO3 module. Collectively, our data shed a new light on the molecular mechanisms underlying wheat defense to Bgt.

Among the three major food crops (rice, wheat and maize), wheat is unique in accumulating gluten proteins in its grains. Of these proteins, the high and low molecular weight glutenin subunits (HMW-GSs and LMW-GSs) form glutenin macropolymers that are vital for the diverse end-uses of wheat grains. In this work, we developed a new series of deletion mutants lacking one or two of the three Glu-1 loci (Glu-A1, -B1 and -D1) specifying HMW-GSs. Comparative analysis of single and double deletion mutants reinforced the suggestion that Glu-D1 (encoding the HMW-GSs 1Dx2 and 1Dy12) has the largest effects on the parameters related to gluten and dough functionalities and breadmaking quality. Consistent with this suggestion, the deletion mutants lacking Glu-D1 or its combination with Glu-A1 or Glu-B1 generally exhibited strong decreases in functional glutenin macropolymers (FGMPs) and in the incorporation of HMW-GSs and LMW-GSs into FGMPs. Further examination of two knockout mutants missing 1Dx2 or 1Dy12 showed that 1Dx2 was clearly more effective than 1Dy12 in promoting FGMPs by enabling the incorporation of more HMW-GSs and LMW-GSs into FGMPs. The new insight obtained and the mutants developed by us may aid further research on the control of wheat end-use quality by glutenin proteins.

In common wheat (Triticum aestivum L.), allelic variations of Glu-A1 locus have important influences on grain end-use quality. Among the three Glu-A1 alleles, Glu-A1a and -A1b encode the high-molecular-weight glutenin subunits (HMW-GSs) 1Ax1 and 1Ax2*, respectively, whereas Glu-A1c does not specify any subunit. Here, we detected a total of 11 Glu-A1 locus haplotypes (H1 to H11) in three wheat species, by developing and using a new set of DNA markers (Xrj5, Xid3, Xrj6, Xid4 and Xrj7). The main haplotypes found in the diploid wheat T. urartu were H1, H4, H5 and H6, with H1 and H4 expressing both 1Ax and 1Ay subunits. The major haplotypes revealed for tetraploid wheat (T. turgidum) were H1, H8 and H9, with the lines expressing both 1Ax and 1Ay belonging to H1, H4 or H7. Four major haplotypes (H1, H9, H10 and H11) were discovered in common wheat, with Glu-A1a associated with H1 and H8, Glu-A1b with H10 or H11, and Glu-A1c with H9. The Glu-A1 locus haplotypes and the new set of DNA markers have potential to be used for more effectively studying and utilizing the molecular variations of Glu-A1 to improve the end-use quality of common wheat are discussed.

Diploid Thinopyrum elongatum ( EE , 2 n = 2 x = 14) and related polyploid species constitute an important gene pool for improving Triticeae grain and forage crops. However, the genomic and molecular marker resources are generally poor for these species. To aid the genetic, molecular, breeding and ecological studies involving Thinopyrum species, we developed a strategy for mining and validating E‐genome‐specific SNP s using Th. elongatum and common wheat ( Triticum aestivum , AABBDD , 2 n = 6 x = 42) as experimental materials. By comparing the transcriptomes between Chinese Spring ( CS , a common wheat variety) and the CS ‐ Th. elongatum octoploid, 35,193 candidate SNP s between E genome genes and their common wheat orthologs were computed. Through comparative genomic analysis, these SNP s were putatively assigned to the seven individual E genome chromosomes. Among 420 randomly selected SNP s, 373 could be validated. Thus, approximately 89% of the mined SNP s may be authentic with respect to their polymorphism and chromosomal location. Using 14 such SNP s as molecular markers, complex E genome introgressions were reliably identified in 78 common wheat‐ Th. elongatum hybrids, and the structural feature of a novel recombinant chromosome formed by 6E and 7E was revealed. Finally, based on testing 33 SNP s assigned to chromosome 3E in multiple genotypes of Th. elongatum , Pseudoroegneria stipifolia (carrying the St genome related to E) and common wheat, we suggest that some of the SNP markers may also be applicable for genetic studies within and among the Thinopyrum species (populations) carrying E and/or St genomes in the future.

Gliadins, specified by six compound chromosomal loci ( Gli-A1/B1/D1 and Gli-A2/B2/D2 ) in hexaploid bread wheat, are the dominant carriers of celiac disease (CD) epitopes. Because of their complexity, genome-wide characterization of gliadins is a strong challenge. Here, we approached this challenge by combining transcriptomic, proteomic and bioinformatic investigations. Through third-generation RNA sequencing, full-length transcripts were identified for 52 gliadin genes in the bread wheat cultivar Xiaoyan 81. Of them, 42 were active and predicted to encode 25 α-, 11 γ-, one δ- and five ω-gliadins. Comparative proteomic analysis between Xiaoyan 81 and six newly-developed mutants each lacking one Gli locus indicated the accumulation of 38 gliadins in the mature grains. A novel group of α-gliadins (the CSTT group) was recognized to contain very few or no CD epitopes. The δ-gliadins identified here or previously did not carry CD epitopes. Finally, the mutant lacking Gli-D2 showed significant reductions in the most celiac-toxic α-gliadins and derivative CD epitopes. The insights and resources generated here should aid further studies on gliadin functions in CD and the breeding of healthier wheat.

In higher plants, L-galactono-1,4-lactone dehydrogenase (GLDH) plays important roles in ascorbic acid (AsA) biosynthesis and assembly of respiration complex I. Here we report three homoeologous genes (TaGLDH-A1, -B1 and -D1) encoding common wheat GLDH isozymes and a unique allelic variant (TaGLDH-A1b) associated with enhanced drought tolerance. TaGLDH-A1, -B1 and -D1 were located on chromosomes 5A, 5B and 5D, respectively, and their transcripts were found in multiple organs. The three homoeologs each conferred increased GLDH activity when ectopically expressed in tobacco. Decreasing TaGLDH expression in wheat significantly reduced GLDH activity and AsA content. TaGLDH-A1b differed from wild type allele TaGLDH-A1a by an in-frame deletion of three nucleotides. TaGLDH-A1b was biochemically less active than TaGLDH-A1a, and the total GLDH activity levels were generally lower in the cultivars carrying TaGLDH-A1b relative to those with TaGLDH-A1a. Interestingly, TaGLDH-A1b cultivars showed stronger water deficiency tolerance than TaGLDH-A1a cultivars, and TaGLDH-A1b co-segregated with decreased leaf water loss in a F2 population. Finally, TaGLDH-A1b cultivars generally exhibited smaller leaf stomatal aperture than TaGLDH-A1a varieties in control or water deficiency environments. Our work provides new information on GLDH genes and function in higher plants. TaGLDH-A1b is likely useful for further studying and improving wheat tolerance to drought stress.

Powdery mildew disease caused by Blumeria graminis f. sp. tritici (Bgt) inflicts severe economic losses in wheat crops. A systematic understanding of the molecular mechanisms involved in wheat resistance to Bgt is essential for effectively controlling the disease. Here, using the diploid wheat Triticum urartu as a host, the genes regulated by immune (IM) and hypersensitive reaction (HR) resistance responses to Bgt were investigated through transcriptome sequencing. Four gene coexpression networks (GCNs) were developed using transcriptomic data generated for 20 T. urartu accessions showing IM, HR or susceptible responses. The powdery mildew resistance regulated (PMRR) genes whose expression was significantly correlated with Bgt resistance were identified, and they tended to be hubs and enriched in six major modules. A wide occurrence of negative regulation of PMRR genes was observed. Three new candidate immune receptor genes (TRIUR3_13045, TRIUR3_01037 and TRIUR3_06195) positively associated with Bgt resistance were discovered. Finally, the involvement of TRIUR3_01037 in Bgt resistance was tentatively verified through cosegregation analysis in a F2 population and functional expression assay in Bgt susceptible leaf cells. This research provides insights into the global network properties of PMRR genes. Potential molecular differences between IM and HR resistance responses to Bgt are discussed.

In higher plants, lipoxygenases (LOXs) catalyze the oxidation of polyunsaturated fatty acids and can accumulate to relatively high levels in the seeds. However, high LOX activity has often been found associated with harmful effects on the quality attributes and the longevity of harvested seeds. Here, we report the development and characterization of three homozygous T5 transgenic lines (designated as LOXRNAi-4, 7 and 9, respectively) with LOX activity specifically reduced in the grains of common wheat. An RNAi hairpin directed under an endosperm-specific promoter was introduced into the genome of the elite wheat variety Longchun 23 using particle bombardment. Each transgenic line (LOXRNAi-4, 7 or 9) derived from separate integration event, which carried more than 20 copies of the transgene. The three LOXRNAi lines and wild-type (WT) Longchun 23 showed a similar level of LOX transcripts in the flag leaves. However, relative to WT control, LOXRNAi-4, 7 and 9 exhibited drastic decreases in the level of LOX transcripts during grain development compared with WT control. The LOX activity levels in the harvested grains of the three transgenic lines were significantly lower than that of WT control under either normal conditions or artificial aging (AA, stored at 40 °C and 85 % humidity for 6 or 9 days) treatment. The whiteness values of the flour samples from LOXRNAi-4, 7 and 9 were generally and significantly higher than those of WT control regardless of the grains were stored under normal or AA conditions. Furthermore, the germination rates of LOXRNAi-4, 7 and 9 were substantially higher than those of WT control under AA treatment. Our data demonstrate that grain-specific reduction in LOX activity by RNAi may represent a generally applicable approach for improving the quality traits and longevity of crop seeds.

In common wheat, insoluble glutenin (IG) is an important fraction of flour glutenin macropolymers, and insoluble glutenin content (IGC) is positively associated with key end-use quality parameters. Here, we present a genetic analysis of the chromosomal loci affecting IGC with the data collected from 90 common wheat varieties cultivated in four environments. Statistical analysis showed that IGC was controlled mainly genetically and influenced by the environment. Among the major genetic components known to affect end-use quality, 1BL/1RS translocation had a significantly negative effect on IGC across all four environments. As to the different alleles of Glu-A1, -B1 and -D1 loci, Glu-A1a, Glu-B1b and Glu-D1d exhibited relatively strong positive effects on IGC in all environments. To identify new loci affecting IGC, association mapping with 1355 DArT markers was conducted. A total of 133 markers were found associated with IGC in two or more environments (P < 0.05), ten of which consistently affected IGC in all four environments. The phenotypic variance explained by the ten markers varied from 4.66% to 8.03%, and their elite alleles performed significantly better than the inferior counterparts in enhancing IGC. Among the ten markers, wPt-3743 and wPt-733835 reflected the action of Glu-D1, and wPt-664972 probably indicated the effect of Glu-A1. The other seven markers, forming three clusters on 2AL, 3BL or 7BL chromosome arms, represented newly identified genetic determinants of IGC. Our work provided novel insights into the genetic control of IGC, which may facilitate wheat end-use quality improvement through molecular breeding in the future.

Roots are essential for normal growth, development, and reproduction of higher plants. Consequently, improvement of root system architecture and functionality is of fundamental importance in crop improvement. However, the genetic mechanisms controlling root morphology and function are still not well understood, especially in common wheat, which possesses a complex and unsequenced hexaploid genome. Here we report a more detailed genetic analysis of qTaLRO-B1, a major quantitative trait locus (QTL) previously detected to affect root length and related traits in common wheat. A pair of QTL isolines with different qTaLRO-B1 alleles was developed. Line 178B, carrying the longer root allele, was significantly more efficient in taking up phosphate nutrient and biomass accumulation than line 178A, with the shorter root allele. We mapped qTaLRO-B1 to a 0.9-cM interval on common wheat chromosome 2BS with seven sequence-tagged-site (STS) markers developed from the genes conserved between wheat and Brachypodium distachyon. The seven STS markers were collinearly conserved in tetraploid wheat, but they covered a much larger genetic distance (22.8 cM) in the latter species. In conclusion, we have converted qTaLRO-B1 into a major gene that affects common wheat root length in a qualitative manner, and improved understanding of the genetic location of qTaLRO-B1 and the chromosomal segment carrying this important locus. The implications of our data for further study of qTaLRO-B1 are discussed.

KEY MESSAGE:Ion beam mutations can be efficiently isolated and deployed for functional comparison of homoeologous loci in polyploid plants, and Glu - 1 loci differ substantially in their contribution to wheat gluten functionality. To efficiently conduct genetic analysis, it is beneficial to have multiple types of mutants for the genes under investigation. Here, we demonstrate that ion beam-induced deletion mutants can be efficiently isolated for comparing the function of homoeologous loci of common wheat (Triticum aestivum). Through fragment analysis of PCR products from M2 plants, ion beam mutants lacking homoeologous Glu-A1, Glu-B1 or Glu-D1 loci, which encode high molecular weight glutenin subunits (HMW-GSs) and affect gluten functionality and end-use quality of common wheat, could be isolated simultaneously. Three deletion lines missing Glu-A1, Glu-B1 or Glu-D1 were developed from the original mutants, with the Glu-1 genomic regions deleted in these lines estimated using newly developed DNA markers. Apart from lacking the target HMW-GSs, the three lines all showed decreased accumulation of low molecular weight glutenin subunits (LMW-GSs) and increased amounts of gliadins. Based on the test data of five gluten and glutenin macropolymer (GMP) parameters obtained with grain samples harvested from two environments, we conclude that the genetic effects of Glu-1 loci on gluten functionality can be ranked as Glu-D1 > Glu-B1 > Glu-A1. Furthermore, it is suggested that Glu-1 loci contribute to gluten functionality both directly (by promoting the formation of GMP) and indirectly (through keeping the balance among HMW-GSs, LMW-GSs and gliadins). Finally, the efficient isolation of ion beam mutations for functional comparison of homoeologous loci in polyploid plants and the usefulness of Glu-1 deletion lines for further studying the contribution of Glu-1 loci to gluten functionality are discussed.

In higher plants, l-galactono-1,4-lactone dehydrogenase (GLDH) participates in the biosynthesis of ascorbic acid (AsA) and the assembly of mitochondrial respiratory complex I. In this work, homozygous Arabidopsis thaliana mutant (gldhRNAi3-11) plants with approximately 40 % of the GLDH activity of wild type (WT) controls were developed by RNA interference, and were found to be viable under standard laboratory conditions. Compared with WT controls, gldhRNAi3-11 plants showed about 20 % decrease in the contents of reduced AsA and total AsA. Like previously recorded for several AsA-deficient mutants (vtc1-1, vtc2-1, vtc3-1 and vtc4-1) grown under long day (LD) conditions, gldhRNAi3-11 plants exhibited an early flowering phenotype in LD environment. Interestingly, relative to WT control, vtc1-1 and vtc4-1, gldhRNAi3-11 had significantly lower leaf water loss rate. Further analysis indicated that reduced stomatal aperture size was likely responsible for the lower water loss displayed by gldhRNAi3-11 leaves. Thus, our work demonstrates that partial suppression of GLDH activity confers significant reduction in leaf water loss through decreasing stomatal aperture size in Arabidopsis. The novel phenotypes displayed by gldhRNAi3-11 plants, the new insights obtained by this work, and their implications on further study of GLDH function in higher plants are discussed.

In higher plants, seed storage proteins (SSPs) are frequently expressed from complex gene families, and allelic variation of SSP genes often affects the quality traits of crops. In common wheat, the Glu-D1 locus, encoding 1Dx and 1Dy SSPs, has multiple alleles. The Glu-D1d allele frequently confers superior end-use qualities to commercial wheat varieties. Here, we studied the haplotype structure of Glu-D1 genomic region and the origin of Glu-D1d. Using seven diagnostic DNA markers, 12 Glu-D1 haplotypes were detected among common wheat, European spelt wheat (T. spelta, a primitive hexaploid relative of common wheat), and Aegilops tauschii (the D genome donor of hexaploid wheat). By comparatively analyzing Glu-D1 haplotypes and their associated 1Dx and 1Dy genes, we deduce that the haplotype carrying Glu-D1d was likely differentiated in the ancestral hexaploid wheat around 10,000 years ago, and was subsequently transmitted to domesticated common wheat and T. spelta. A group of relatively ancient Glu-D1 haplotypes was discovered in Ae. tauschii, which may serve for the evolution of other haplotypes. Moreover, a number of new Glu-D1d variants were found in T. spelta. The main steps in Glu-D1d differentiation are proposed. The implications of our work for enhancing the utility of Glu-D1d in wheat quality improvement and studying the SSP alleles in other crop species are discussed.

Grain weight, an essential yield component, is under strong genetic control and markedly influenced by the environment. Here, by genome-wide association analysis with a panel of 94 elite common wheat varieties, 37 loci were found significantly associated with thousand-grain weight (TGW) in one or more environments differing in water and fertiliser levels. Five loci were stably associated with TGW under all 12 environments examined. Their elite alleles had positive effects on TGW. Four, two, three, and two loci were consistently associated with TGW in the irrigated and fertilised (IF), rainfed (RF), reduced nitrogen (RN), and reduced phosphorus (RP) environments. The elite alleles of the IF-specific loci enhanced TGW under well-resourced conditions, whereas those of the RF-, RN-, or RP-specific loci conferred tolerance to the TGW decrease when irrigation, nitrogen, or phosphorus were reduced. Moreover, the elite alleles of the environment-independent and -specific loci often acted additively to enhance TGW. Four additional loci were found associated with TGW in specific locations, one of which was shown to contribute to the TGW difference between two experimental sites. Further analysis of 14 associated loci revealed that nine affected both grain length and width, whereas the remaining loci influenced either grain length or width, indicating that these loci control grain weight by regulating kernel size. Finally, the elite allele of Xpsp3152 frequently co-segregated with the larger grain haplotype of TaGW2-6A, suggesting probable genetic and functional linkages between Xpsp3152 and GW2 that are important for grain weight control in cereal plants. Our study provides new knowledge on TGW control in elite common wheat lines, which may aid the improvement of wheat grain weight trait in further research.

Polyphenol oxidase (PPO) plays multiple roles in plant growth and responses to environmental stimuli. However, there is still little molecular information on PPO genes in sorghum. Here, eight distinct PPO gene members, designated as SbPPO1–SbPPO8, were identified in two grain sorghum genotypes, i.e., BTx623 and Henong 16 (HN16). The eight members were located on sorghum chromosomes 3 (SbPPO1 and SbPPO2), 6 (SbPPO3 and SbPPO4), 7 (SbPPO5–SbPPO7), or 10 (SbPPO8) and contained zero (SbPPO6–SbPPO8), one (SbPPO1, SbPPO2, and SbPPO5), or two (SbPPO3 and SbPPO4) introns. In BTx623, the deduced proteins of SbPPO1–SbPPO8 all contained an intact binuclear copper center required for enzyme activity, as well as the tyrosine motif and its interacting residues involved in structural maintenance. SbPPO2–SbPPO6 were found to possess thylakoid transfer domains, whereas SbPPO1 and SbPPO8 were predicted to contain N-terminal signal peptides for targeting to the secretory pathway. In HN16, the SbPPO3 allele was a pseudogene, whereas the remaining seven SbPPO alleles showed high identities with their counterparts in BTx623. Phylogenetically, sorghum PPO genes generally exhibited relationships closer to those of maize, and the maize orthologues of SbPPO2–SbPPO8 could be recognized by synteny analysis. Finally, SbPPO5 was found to be the major expressed member at the early stage of grain growth, and the dynamic change of SbPPO5 transcript level paralleled that of the total PPO activity during the grain development in both BTx623 and HN16. Our study generated new information on the PPO members in sorghum, which may facilitate more detailed functional analysis of these important genes in further research.

In this work, we conducted functional analysis of Arabidopsis HRS1 gene in order to provide new insights into the mechanisms governing seed germination. Compared with wild type (WT) control, HRS1 knockout mutant (hrs1-1) exhibited significant germination delays on either normal medium or those supplemented with abscisic acid (ABA) or sodium chloride (NaCl), with the magnitude of the delay being substantially larger on the latter media. The hypersensitivity of hrs1-1 germination to ABA and NaCl required ABI3, ABI4 and ABI5, and was aggravated in the double mutant hrs1-1abi1-2 and triple mutant hrs1-1hab1-1abi1-2, indicating that HRS1 acts as a negative regulator of ABA signaling during seed germination. Consistent with this notion, HRS1 expression was found in the embryo axis, and was regulated both temporally and spatially, during seed germination. Further analysis showed that the delay of hrs1-1 germination under normal conditions was associated with reduction in the elongation of the cells located in the lower hypocotyl (LH) and transition zone (TZ) of embryo axis. Interestingly, the germination rate of hrs1-1 was more severely reduced by the inhibitor of cell elongation, and more significantly decreased by the suppressors of plasmalemma H+-ATPase activity, than that of WT control. The plasmalemma H+-ATPase activity in the germinating seeds of hrs1-1 was substantially lower than that exhibited by WT control, and fusicoccin, an activator of this pump, corrected the transient germination delay of hrs1-1. Together, our data suggest that HRS1 may be needed for suppressing ABA signaling in germinating embryo axis, which promotes the timely germination of Arabidopsis seeds probably by facilitating the proper function of plasmalemma H+-ATPase and the efficient elongation of LH and TZ cells.

Background Phosphomannomutase (PMM) is an essential enzyme in eukaryotes. However, little is known about PMM gene and function in crop plants. Here, we report molecular evolutionary and biochemical analysis of PMM genes in bread wheat and related Triticeae species. Results Two sets of homoeologous PMM genes ( TaPMM-1 and 2 ) were found in bread wheat, and two corresponding PMM genes were identified in the diploid progenitors of bread wheat and many other diploid Triticeae species. The duplication event yielding PMM-1 and 2 occurred before the radiation of diploid Triticeae genomes. The PMM gene family in wheat and relatives may evolve largely under purifying selection. Among the six TaPMM genes, the transcript levels of PMM-1 members were comparatively high and their recombinant proteins were all enzymatically active. However, PMM-2 homoeologs exhibited lower transcript levels, two of which were also inactive. TaPMM-A1, B1 and D1 were probably the main active isozymes in bread wheat tissues. The three isozymes differed from their counterparts in barley and Brachypodium distachyon in being more tolerant to elevated test temperatures. Conclusion Our work identified the genes encoding PMM isozymes in bread wheat and relatives, uncovered a unique PMM duplication event in diverse Triticeae species, and revealed the main active PMM isozymes in bread wheat tissues. The knowledge obtained here improves the understanding of PMM evolution in eukaryotic organisms, and may facilitate further investigations of PMM function in the temperature adaptability of bread wheat.