Recognizing the hidden half in wheat: root system attributes associated with drought tolerance.

Improving drought tolerance in wheat is crucial for maintaining productivity and food security. Roots are responsible for the uptake of water from soil, and a number of root traits are associated with drought tolerance. Studies have revealed many quantitative trait loci and genes controlling root development in plants. However, the genetic dissection of root traits in response to drought in wheat is still unclear. Here, we review crop root traits associated with drought, key genes governing root development in plants, and quantitative trait loci and genes regulating root system architecture under water-limited conditions in wheat. Deep roots, optimal root length density and xylem diameter, and increased root surface area are traits contributing to drought tolerance. In view of the diverse environments in which wheat is grown, the balance among root and shoot traits, as well as individual and population performance, are discussed. The known functions of key genes provide information for the genetic dissection of root development of wheat in a wide range of conditions, and will be beneficial for molecular marker development, marker-assisted selection, and genetic improvement in breeding for drought tolerance.

Genetic insights into natural variation underlying salt tolerance in wheat.

Developing salt-tolerant crop varieties is one of the important approaches to cope with increasing soil salinization worldwide. In this study, a diversity panel of 323 wheat accessions and 150 doubled haploid lines were phenotyped for salt-responsive morphological and physiological traits across two growth stages. The comprehensive salt tolerance of each wheat accession was evaluated based on principal component analysis. A total of 269 associated loci for salt-responsive traits and/or salt tolerance indices were identified by genome-wide association studies using 395 675 single nucleotide polymorphisms, among which 22 overlapping loci were simultaneously identified by biparental quantitative trait loci mapping. Two novel candidate genes ROOT NUMBER 1 (TaRN1) and ROOT NUMBER 2 (TaRN2) involved in root responses to salt stress fell within overlapping loci, showing different expression patterns and a frameshift mutation (in TaRN2) in contrasting salt-tolerant wheat genotypes. Moreover, the decline in salt tolerance of Chinese wheat varieties was observed from genetic and phenotypic data. We demonstrate that a haplotype controlling root responses to salt stress has been diminished by strong selection for grain yield, which highlights that linkage drag constrains the salt tolerance of Chinese wheat. This study will facilitate salt-tolerant wheat breeding in terms of elite germplasm, favorable alleles and selection strategies.

RING finger ubiquitin E3 ligase gene TaSDIR1-4A contributes to determination of grain size in common wheat.

Salt and drought-induced RING finger1 (SDIR1) is a RING-type E3 ubiquitin ligase that plays a key role in ABA-mediated responses to salinity and drought stress via the ubiquitination pathway in some plant species. However, its function in wheat (Triticum aestivum) is unknown. Here, we isolated a SDIR1 member in wheat, TaSDIR1-4A, and characterized its E3 ubiquitin ligase activity. DNA polymorphism assays showed the presence of two nucleotide variation sites in the promoter region of TaSDIR1-4A, leading to the detection of the haplotypes Hap-4A-1 and Hap-4A-2 in wheat populations. Association analysis showed that TaSDIR1-4A haplotypes were associated with 1000-grain weight (TGW) across a variety of different environments, including well-watered and heat-stress conditions. Genotypes with Hap-4A-2 had higher TGW than those with Hap-4A-1. Phenotypes in both gene-silenced wheat and transgenic Arabidopsis showed that TaSDIR1-4A was a negative regulator of grain size. Gene expression assays indicated that TaSDIR1-4A was most highly expressed in flag leaves, and expression was higher in Hap-4A-1 accessions than in Hap-4A-2 accessions. The difference might be attributable to the fact that TaERF3 (ethylene response factor) can act as a transcriptional repressor of TaSDIR1-4A in Hap-4A-2 but not in Hap-4A-1. Examination of modern wheat varieties shows that the favorable haplotype has been positively selected in breeding programs in China. The functional marker for TaSDIR1-4A developed in this study should be helpful for future wheat breeding.

Identification of TaPPH-7A haplotypes and development of a molecular marker associated with important agronomic traits in common wheat.

BACKGROUND: Premature senescence of flag leaf severely affects wheat yield and quality. Chlorophyll (Chl) degradation is the most obvious symptom during leaf senescence and catalyzed by a series of enzymes. Pheophytin pheophorbide hydrolase (Pheophytinase, PPH) gene encodes a Chl degradation hydrolase. RESULTS: In this study, the coding, genomic and promoter sequences of wheat TaPPH-A gene were cloned. The corresponding lengths were 1467 bp, 4479 bp and 3666 bp, respectively. Sequence structure analysis showed that TaPPH-A contained five exons and four introns. After the multiple sequences alignment of TaPPH-A genome from 36 accessions in a wheat diversity panel, four SNPs and one 2-bp InDel were observed, which formed two haplotypes, TaPPH-7A-1 and TaPPH-7A-2. Based on the SNP at 1299 bp (A/G), a molecular marker TaPPH-7A-dCAPS was developed to distinguish allelic variation (A/G). Using the molecular markers, 13 SSR, and 116 SNP markers, a linkage map of chromosome 7A were integrated. TaPPH-A was mapped on the chromosome region flanked by Xwmc9 (0.94 cM) and AX-95634545 (1.04 cM) on 7A in a DH population. Association analysis between TaPPH-7A allelic variation and agronomic traits found that TaPPH-7A was associated with TGW in 11 of 12 environments and Chl content at grain-filling stage under drought stress using Population 1 consisted of 323 accessions. The accessions possessed TaPPH-7A-1 (A) had higher TGW and Chl content than those possessed TaPPH-7A-2 (G), thus TaPPH-7A-1 (A) was a favorable allelic variation. By analyzing the frequency of favorable allelic variation TaPPH-7A-1 (A) in Population 2 with 157 landraces and Population 3 with 348 modern cultivars, we found it increased from pre-1950 (0) to 1960s (54.5%), then maintained a relatively stable level about 56% from 1960s to 1990s. CONCLUSION: These results suggested the favorable allelic variation TaPPH-7A-1 (A) should be valuable in enhancing grain yield by improving the source (chlorophyll content) and sink (the developing grain) simultaneously. Furthermore, the newly developed molecular marker TaPPH-7A-dCAPS could be integrated into a breeding kit of screening high TGW wheat for marker-assisted selection.

Genetic dissection of drought and heat-responsive agronomic traits in wheat.

High yield and wide adaptation are principal targets of wheat breeding but are hindered by limited knowledge on genetic basis of agronomic traits and abiotic stress tolerances. In this study, 277 wheat accessions were phenotyped across 30 environments with non-stress, drought-stressed, heat-stressed, and drought-heat-stressed treatments and were subjected to genome-wide association study using 395 681 single nucleotide polymorphisms. We detected 295 associated loci including consistent loci for agronomic traits across different treatments and eurytopic loci for multiple abiotic stress tolerances. A total of 22 loci overlapped with quantitative trait loci identified by biparental quantitative trait loci mapping. Six loci were simultaneously associated with agronomic traits and abiotic stress tolerance, four of which fell within selective sweep regions. Selection in Chinese wheat has increased the frequency of superior marker alleles controlling yield-related traits in the four loci during past decades, which conversely diminished favourable genetic variation controlling abiotic stress tolerance in the same loci; two promising candidate paralogous genes colocalized with such loci, thereby providing potential targets for studying the molecular mechanism of stress tolerance-productivity trade-off. These results uncovering promising alleles controlling agronomic traits and/or multiple abiotic stress tolerances, providing insights into heritable covariation between yield and abiotic stress tolerance, will accelerate future efforts for wheat improvement.

A wheat protein kinase gene TaSnRK2.9-5A associated with yield contributing traits.

KEY MESSAGE: We developed breeder-friendly high-throughput and cost-effective KASP marker for marker-assisted selection for grain yield related traits in wheat. Plant-specific protein kinase, SnRK2s, is a major family of signaling genes associated with metabolic regulations, nutrient utilization and response to external stimuli. In the present study, three copies of TaSnRK2.9 were isolated from chromosomes 5A, 5B and 5D of wheat (Triticum aestivum L.). The coding regions of TaSnRK2.9-5A, TaSnRK2.9-5B and promoter region of TaSnRK2.9-5D were investigated for sequence polymorphism. Single nucleotide polymorphisms (SNPs) were identified for TaSnRK2.9-5A, while no polymorphism was identified in TaSnRK2.9-5B and TaSnRK2.9-5D. The nucleotide sequence of TaSnRK2.9-5A consisted of 2180 bp having eight introns and nine exons. Three SNPs were identified at 308 nt, 698 nt and 1700 nt. For high-throughput genotyping, two kompetitive allele-specific PCR (KASP) markers were developed. Four haplotypes Hap-5A-1, Hap-5A-2, Hap-5A-3 and Hap-5A-4 were detected in wheat populations collected from China, Europe and Pakistan. Association analysis was performed with mixed linear model in TASSEL (v 5.0). The results indicated that Hap-5A-1/2 of TaSnRK2.9-5A were significantly associated with high thousand kernel weight, while Hap-5A-4 with high grains per spike. Overexpressing transgenic rice also showed higher grains per spike which is in accordance with association analysis results. Geographic distribution and allelic frequency indicted that the favored haplotypes were positively selected in Chinese (Hap-5A-1/2), Pakistani (Hap-5A-1), east European (Hap-5A-1) and west European (Hap-5A-4) wheat breeding. The results suggest that the developed KASP markers can be utilized in yield improvement by marker-assisted selection in wheat breeding.

TaARF4 genes are linked to root growth and plant height in wheat.

BACKGROUND AND AIMS: Auxin response factors (ARFs) as transcription activators or repressors have important roles in plant growth and development, but knowledge about the functions of wheat ARF members is limited. A novel ARF member in wheat (Triticum aestivum), TaARF4, was identified, and its protein function, haplotype geographic distribution and allelic frequencies were investigated. METHODS: Tissue expression of TaARF4 was analysed by real-time PCR. Sub-cellular localization was performed using green fluorescent protein (GFP)-tagged TaARF4. Ectopic expression of TaARF4-A in arabidopsis was used to study its functions. Electrophoretic mobility shift assays (EMSAs), chromatin immunoprecipitation (ChIP) analyses and gene expression were performed to detect TaARF4 target genes. A dCAPS (derived cleaved amplified polymorphic sequence) marker developed from TaARF4-B was used to identify haplotypes and association analysis between haplotypes and agronomic traits. KEY RESULTS: TaARF4-A was constitutively expressed and its protein was localized in the nucleus. Ectopic expression of TaARF4-A in arabidopsis caused abscisic acid (ABA) insensitivity, shorter primary root length and reduced plant height (PH). Through expression studies and ChIP assays, TaARF4-A was shown to regulate HB33 expression which negatively responded to ABA, and reduced root length and plant height by repressing expression of Gretchen Hagen 3 (GH3) genes that in turn upregulated indole-3-acetic acid content in arabidopsis. Association analysis showed that TaARF4-B was strongly associated with PH and root depth at the tillering, jointing and grain fill stages. Geographic distribution and allelic frequencies suggested that TaARF4-B haplotypes were selected in Chinese wheat breeding programmes. An amino acid change (threonine to alanine) at position 158 might be the cause of phenotype variation in accessions possessing different haplotypes. CONCLUSIONS: Ectopic expression and association analysis indicate that TaARF4 may be involved in root length and plant height determination in wheat. This work is helpful for selection of wheat genotypes with optimal root and plant architecture.

Genome-wide association study reveals genomic regions controlling root and shoot traits at late growth stages in wheat.

BACKGROUND AND AIMS: Root system morphology is important for sustainable agriculture, but the genetic basis of root traits and their relationship to shoot traits remain to be elucidated. The aim of the present study was to dissect the genetic basis of root traits at late growth stages and its implications on shoot traits in wheat. METHODS: Among 323 wheat accessions, we investigated phenotypic differences in root traits at booting and mid-grain fill stages in PVC tubes, shoot traits including plant height (PH), canopy temperature (CT) and grain yield per plant (YPP) in a field experiment, and performed a genome-wide association study with a Wheat 660K SNP Array. KEY RESULTS: Deep-rooted accessions had lower CT and higher YPP than those with shallow roots, but no significant relationship was identified between root dry weight and shoot traits. Ninety-three significantly associated loci (SALs) were detected by the mixed linear model, among which three were hub SALs (Co-6A, Co-6B and Co-6D) associated with root depth at both booting and mid-grain fill stages, as well as CT and YPP. Minirhizotron system scanning results suggested that the causal genes in the three SALs may regulate root elongation in the field. The heritable independence between root depth and PH was demonstrated by linkage disequilibrium analysis. The YPP was significantly higher in genotypes which combined favourable marker alleles (FMAs) for root depth and PH, suggesting that a deep root and shorter plant height are suitable traits for pyramiding target alleles by molecular marker-assisted breeding. CONCLUSIONS: These results uncovered promising genomic regions for functional gene discovery of root traits in the late growth period, enhanced understanding of correlation between root and shoot traits, and will facilitate intensive study on root morphology and breeding through molecular design.

Functional Conservation and Divergence among Homoeologs of TaSPL20 and TaSPL21, Two SBP-Box Genes Governing Yield-Related Traits in Hexaploid Wheat.

Maintaining high and stable yields has become an increasing challenge in wheat breeding due to climate change. Although Squamosa-promoter binding protein (SBP)-box genes have important roles in plant development, very little is known about the actual biological functions of wheat SBP-box family members. Here, we dissect the functional conservation, divergence, and exploitation of homoeologs of two paralogous TaSPL wheat loci during domestication and breeding. TaSPL20 and TaSPL21 were highly expressed in the lemma and palea. Ectopic expressions of TaSPL20/21 in rice exhibited similar functions in terms of promoting panicle branching but had different functions during seed development. We characterized all six TaSPL20/21 genes located across the three homoeologous (A, B, and D) genomes. According to the functional analysis of naturally occurring variants in 20 environments, four favorable haplotypes were identified. Together, they reduced plant height by up to 27.5%, and TaSPL21-6D-HapII increased 1000-grain weight by 9.73%. Our study suggests that TaSPL20 and TaSPL21 homoeologs underwent diversification in function with each evolving its own distinctive characteristics. During domestication and breeding of wheat in China, favorable haplotypes of each set were selected and exploited to varying degrees due to their large effects on plant height and 1000-grain weight.

Overexpression of wheat gene TaMOR improves root system architecture and grain yield in Oryza sativa.

Improved root architecture is an effective strategy to increase crop yield. We demonstrate that overexpression of transcription factor gene MORE ROOT (TaMOR) from wheat (Triticum aestivum L.) results in more roots and higher grain yield in rice (Oryza sativa). TaMOR, encoding a plant-specific transcription factor belonging to the ASYMMETRIC LEAVES2/LATERAL ORGAN BOUNDARIES (AS2/LOB) protein family, is highly conserved in wheat and its wild relatives. In this study, tissue expression patterns indicated that TaMOR mainly localizes to root initiation sites. The consistent gene expression pattern suggests that TaMOR is involved in root initiation. Exogenous auxin treatment induced TaMOR expression without de novo protein biosynthesis. Both in vivo and in vitro experiments demonstrated that TaMOR interacts with TaMOR-related protein TaMRRP, which contains a four-tandem-pentatricopeptide repeat motif. Overexpression of TaMOR led to more lateral roots in Arabidopsis thaliana, and TaMOR-overexpressing rice plants had more crown roots, a longer main panicle, a higher number of primary branches on the main panicle, a higher grain number per plant, and higher yield per plant than the plants of wild type. In general, TaMOR-D-overexpressing lines had larger root systems in Arabidopsis and rice, and produce a higher grain yield per plant. TaMOR therefore offers an opportunity to improve root architecture and increase yield in crop plants.

TEF-7A, a transcript elongation factor gene, influences yield-related traits in bread wheat (Triticum aestivum L.).

In this study, TaTEF-7A, a member of the transcript elongation factor gene family, and its flanking sequences were isolated. TaTEF-7A was located on chromosome 7A and was flanked by markers Xwmc83 and XP3156.3. Subcellular localization revealed that TaTEF-7A protein was localized in the nucleus. This gene was expressed in all organs, but the highest expression occurred in young spikes and developing seeds. Overexpression of TaTEF-7A in Arabidopsis thaliana produced pleiotropic effects on vegetative and reproductive development that enhanced grain length, silique number, and silique length. No diversity was found in the coding region of TaTEF-7A, but 16 single nucleotide polymorphisms and Indels were detected in the promoter regions of different cultivars. Markers based on sequence variations in the promoter regions (InDel-629 and InDel-604) were developed, and three haplotypes were identified based on those markers. Haplotype-trait association analysis of the Chinese wheat mini core collection revealed that TaTEF-7A was significantly associated with grain number per spike. Phenotyping of near-isogenic lines (NILs) confirmed that TaTEF-7A increases potential grain yield and yield-related traits. Frequency changes in favoured haplotypes gradually increased in cultivars released in China from the 1940s. Geographic distributions of favoured haplotypes were characterized in six major wheat production regions worldwide. The presence of Hap-7A-3, the favoured haplotype, showed a positive correlation with yield in a global set of breeding lines. These results suggest that TaTEF-7A is a functional regulatory factor for grain number per spike and provide a basis for marker-assisted selection.

Genetic dissection of developmental behavior of grain weight in wheat under diverse temperature and water regimes.

As a quantitatively inherited trait related to high yield potential, grain weight (GW) development in wheat is constrained by abiotic stresses such as limited water supply and high temperature. Data from a doubled haploid population, derived from a cross of (Hanxuan 10 × Lumai 14), grown in four environments were used to explore the genetic basis of GW developmental behavior in unconditional and conditional quantitative trait locus (QTL) analyses using a mixed linear model. Thirty additive QTLs and 41 pairs of epistatic QTLs were detected, and were more frequently observed on chromosomes 1B, 2A, 2D, 4A, 4B and 7B. No single QTL was continually active during all stages or periods of grain growth. The QTLs with additive effects (A-QTLs) expressed in the period S1|S0 (the period from the flowering to the seventh day after) formed a foundation for GW development. GW development at these stages can be used as an index for screening superior genotypes under diverse abiotic stresses in a wheat breeding program. One QTL, i.e. Qgw.cgb-6A.2, showed high adaptability for water-limited and heat-stress environments. Many A-QTLs interacted with more than one other QTL in the two genetic models, such as Qgw.cgb-4B.2 interacted with five QTLs, showing that the genetic architecture underlying GW development involves a collective expression of genes with additive and epistatic effects.

Association mapping of dynamic developmental plant height in common wheat.

Drought as a major abiotic stress often occurs from stem elongation to the grain filling stage of wheat in northern China. Plant height (PH) is a suitable trait to model the dissection of drought tolerance. The purposes of the present study were to validate molecular markers for PH developmental behavior and identify elite alleles of molecular markers. After the phenotyping of 154 accessions for PH dynamic development under well-watered (WW) and drought stressed (DS) conditions, and the genotyping of 60 SSR markers from six candidate chromosome regions related to PH found in our previous linkage mapping studies, both parameters PH and drought tolerance coefficient (DTC) calculated by the conditional analysis were used for association mapping. A total of 46 significant association signals (P < 0.01) were identified in 23 markers, and phenotypic variation ranged from 7 to 50%. Among them, four markers Xgwm261-2D, Xgwm495-4B, Xbarc109-4B and Xcfd23-4D were detected under both water regimes. Furthermore, 10 markers were associated with DTC, and four with both parameters PH and DTC at the same plant development stage. The results revealed different allelic effects of associated markers; for example, the 155 bp Xgwm495-4B allele was associated with a reduced height of -11.2 cm under DS and -15.3 cm under WW, whereas the 167 bp allele exhibited increased height effects of 3.9 and 8.1 cm, respectively. This study demonstrates a strong power of joint association analysis and linkage mapping for the identification of important genes in wheat.

TaABC1, a member of the activity of bc1 complex protein kinase family from common wheat, confers enhanced tolerance to abiotic stresses in Arabidopsis.

Abiotic stresses such as drought, salinity, and low temperature have drastic effects on plant growth and development. However, the molecular mechanisms regulating biochemical and physiological changes in response to stresses are not well understood. Protein kinases are major signal transduction factors among the reported molecular mechanisms mediating acclimation to environmental changes. Protein kinase ABC1 (activity of bc(1) complex) is involved in regulating coenzyme Q biosynthesis in mitochondria in yeast (Saccharomyces cersvisiae), and in balancing oxidative stress in chloroplasts in Arabidopsis thaliana. In the current study, TaABC1 (Triticum aestivum L. activity of bc(1) complex) protein kinase was localized to the cell membrane, cytoplasm, and nucleus. The effects of overexpressing TaABC1 in transgenic Arabidopsis plants on responses to drought, salt, and cold stress were further investigated. Transgenic Arabidopsis overexpressing the TaABC1 protein showed lower water loss and higher osmotic potential, photochemistry efficiency, and chlorophyll content, while cell membrane stability and controlled reactive oxygen species homeostasis were maintained. In addition, overexpression of TaABC1 increased the expression of stress-responsive genes, such as DREB1A, DREB2A, RD29A, ABF3, KIN1, CBF1, LEA, and P5CS, detected by real-time PCR analysis. The results suggest that TaABC1 overexpression enhances drought, salt, and cold stress tolerance in Arabidopsis, and imply that TaABC1 may act as a regulatory factor involved in a multiple stress response pathways.

Characterization of a common wheat (Triticum aestivum L.) TaSnRK2.7 gene involved in abiotic stress responses.

Sucrose non-fermenting-1-related protein kinase 2 (SnRK2) plays a key role in the plant stress signalling transduction pathway via phosphorylation. Here, a SnRK2 member of common wheat, TaSnRK2.7, was cloned and characterized. Southern blot analysis suggested that the common wheat genome contains three copies of TaSnRK2.7. Subcellular localization showed the presence of TaSnRK2.7 in the cell membrane, cytoplasm, and nucleus. Expression patterns revealed that TaSnRK2.7 is expressed strongly in roots, and responds to polyethylene glycol, NaCl, and cold stress, but not to abscisic acid (ABA) application, suggesting that TaSnRK2.7 might participate in non-ABA-dependent signal transduction pathways. TaSnRK2.7 was transferred to Arabidopsis under the control of the CaMV-35S promoter. Function analysis showed that TaSnRK2.7 is involved in carbohydrate metabolism, decreasing osmotic potential, enhancing photosystem II activity, and promoting root growth. Its overexpression results in enhanced tolerance to multi-abiotic stress. Therefore, TaSnRK2.7 is a multifunctional regulatory factor in plants, and has the potential to be utilized in transgenic breeding to improve abiotic stress tolerance in crop plants.

Genetic diversity analysis of abiotic stress response gene TaSnRK2.7-A in common wheat.

Sucrose non-fermenting1-related protein kinase 2 (SnRK2) plays a key role in plant stress signaling transduction pathways. In this study, one copy of TaSnRK2.7, a SnRK2 member of common wheat, was isolated and characterized for nucleotide diversity among 45 wheat accessions with different stress-response features. Most of the accessions were elite wheat cultivars, which had been subject to population bottlenecks and intensive selection during breeding. Nucleotide and haplotype diversity across the entire TaSnRK2.7-A region was 0.00076 and 0.590, respectively, and diversity in non-coding regions was higher than that in coding regions. Sliding-window analysis showed variable levels of nucleotide variation along the entire TaSnRK2.7-A region; the sixth intron and ninth exon represented variation-enriched regions. As predicted, neutrality tests revealed that population bottlenecks or purifying selection had acted on the TaSnRK2.7-A gene, a relatively conserved gene. Furthermore, strong linkage disequilibrium between SNP loci extends across the entire TaSnRK2.7-A region. These findings demonstrate that the TaSnRK2.7-A genomic region has evolved under extensive selection pressure during crop breeding.

Genetic analysis of carbon isotope discrimination and its relation to yield in a wheat doubled haploid population.

Carbon isotope discrimination (Δ(13)C) is considered a useful indicator for indirect selection of grain yield (GY) in cereals. Therefore, it is important to evaluate the genetic variation in Δ(13)C and its relationship with GY. A doubled haploid (DH) population derived from a cross of two common wheat varieties, Hanxuan 10 (H10) and Lumai 14 (L14), was phenotyped for Δ(13)C in the flag leaf, GY and yield associated traits in two trials contrasted by water availability, specifically, rain-fed and irrigated. Quantitative trait loci (QTLs) were identified by single locus and two locus QTL analyses. QTLs for Δ(13)C were located on chromosomes 1A, 2B, 3B, 5A, 7A and 7B, and QTLs for other traits on all chromosomes except 1A, 4D, 5A, 5B and 6D. The population selected for high Δ(13)C had an increased frequency of QTL for high Δ(13)C, GY and number of spikes per plant (NSP) when grown under rain-fed conditions and only for high Δ(13)C and NSP when grown under irrigated conditions, which was consistent with agronomic performance of the corresponding trait values in the high Δ(13)C progeny; that is, significantly greater than that in the low Δ(13)C. Therefore, selection for Δ(13)C was beneficial in increasing grain yield in rain-fed environments.

Cloning and Characterization of TaSAP7-A, a Member of the Stress-Associated Protein Family in Common Wheat.

Stress association proteins (SAPs) are A20/AN1 zinc-finger domain proteins, which play important roles in plant adaptation to abiotic stress and plant development. The functions of SAPs in some plants were reported, but little is known about it in wheat (Triticum aestivum L.). In this study, we characterized a novel 2AN1-type stress association protein gene TaSAP7-A, which was mapped to chromosome 5A in wheat. Subcellular localization indicated that TaSAP7-A was distributed in the nucleus and cytoplasm. Unlike previously known A20/AN1-type SAP genes, TaSAP7-A was negatively regulated to abiotic stress tolerance. Overexpressing TaSAP7-A Arabidopsis lines were hypersensitive to ABA, osmotic and salt stress at germination stage and post-germination stage. Overexpression of TaSAP7-A Arabidopsis plants accelerated the detached leaves' chlorophyll degradation. Association analysis of TaSAP7-A haplotypes and agronomic traits showed that Hap-5A-2 was significantly associated with higher chlorophyll content at jointing stage and grain-filling stage. These results jointly revealed that TaSAP7-A is related to the chlorophyll content in the leaves of Arabidopsis and wheat. Both in vivo and in vitro experiments demonstrated that TaSAP7-A interacted with TaS10B, which was the component of regulatory subunit in 26S proteasome. In general, TaSAP7-A was a regulator of chlorophyll content, and favorable haplotypes should be helpful for improving plant chlorophyll content and grain yield of wheat.

Association Analysis Revealed That TaPYL4 Genes Are Linked to Plant Growth Related Traits in Multiple Environment.

Abscisic acid (ABA), one of phytohormones, plays an important regulatory role in plant growth and development. ABA receptor PYL4 (pyrabactin resistance 1-like 4) was previously detected to be involved in plant response to a variety of stresses. TaPYL4 overexpression could enhance wheat (Triticum aestivum) drought resistance. In order to further investigate TaPYL4's role in regulating development of other major agronomic traits in wheat, genes of TaPYL4-2A, TaPYL4-2B, and TaPYL4-2D were cloned from wheat, respectively. Polymorphism analysis on TaPYL4 sequences revealed that encoding regions of the three genes were highly conserved, without any SNP (single nucleotide polymorphism) presence. However, nine SNPs and four SNPs were identified in the promoter regions of TaPYL4-2A and TaPYL4-2B, respectively. Functional molecular markers were developed based on these polymorphisms, which were then used to scan a natural population of 323 common wheat accessions for correlation analysis between genotype and the target phenotypic traits. Both TaPYL4-2A and TaPYL4-2B markers were significantly correlated with plant growth-related traits under multiple environments (well-watered, drought and heat stress treatments). The additive effects of TaPYL4-2A and TaPYL4-2B were verified by the combinational haplotype (Hap-AB1∼Hap-AB4) effects determined from field data. Cis-acting elements were analyzed in the promoters of TaPYL4-2A and TaPYL4-2B, showing that a TGA-element bound by ARFs (auxin response factors) existed only in Hap-2A-1 of TaPYL4-2A. Gene expression assays indicated that TaPYL4-2A was constitutively expressed in various tissues, with higher expression in Hap-2A-1 genotypes than in Hap-2A-2 materials. Notably, TaARF4 could act as TaPYL4-2A transcription activator in Hap-2A-1 materials, but not in Hap-2A-2 genotypes. Analysis of geographic distribution and temporal frequency of haplotypes indicated that Hap-AB1 was positively selected in wheat breeding in China. Therefore, TaPYL4-2A and TaPYL4-2B could be a valuable target gene in wheat genetic improvement to develop the ideal plant architecture.

Genetic dissection of the developmental behaviours of plant height in wheat under diverse water regimes.

Plant height (PH), a crucial trait related to yield potential in crop plants, is known to be typically quantitatively inherited. However, its full expression can be inhibited by a limited water supply. In this study, the genetic basis of the developmental behaviour of PH was assessed in a 150-line wheat (Triticum aestivum L.) doubled haploid population (Hanxuan 10 x Lumai 14) grown in 10 environments (year x site x water regime combinations) by unconditional and conditional quantitative trait locus (QTL) analyses in a mixed linear model. Genes that were expressed selectively during ontogeny were identified. No single QTL was continually active in all periods of PH growth, and QTLs with additive effects (A-QTLs) expressed in the period S1|S0 (the period from the original point to the jointing stage) formed a foundation for PH development. Additive main effects (a effects), which were mostly expressed in S1|S0, were more important than epistatic main effects (aa effects) or QTL x environment interaction (QE) effects, suggesting that S1|S0 was the most significant development period affecting PH growth. A few QTLs, such as QPh.cgb-6B.7, showed high adaptability for water-limited environments. Many QTLs, including four A-QTLs (QPh.cgb-2D.1, QPh.cgb-4B.1, QPh.cgb-4D.1, and QPh.cgb-5A.7) coincident with previously identified reduced height (Rht) genes (Rht8, Rht1, Rht2, and Rht9), interacted with more than one other QTL, indicating that the genetic architecture underlying PH development is a network of genes with additive and epistatic effects. Therefore, based on multilocus combinations in S1|S0, superior genotypes were predicted for guiding improvements in breeding for PH.