Zhengqiang Ma

Molecular genetic analysis of five spike-related traits in wheat using RIL and immortalized F2 populations

Kernel number per spike is one of the most important yield components of wheat. To map QTLs related to kernel number including spike length (SPL), spikelet number per spike (SPN), fertile spikelet number (FSPN), sterile spikelet number (SSPN) and compactness, and to characterize the inheritance modes of the QTLs and two-locus interactions, 136 recombinant inbred lines (RILs) derived from ‘Nanda2419’ x ‘Wangshuibai’ and an immortalized F2 population (IF2) generated by randomly permutated intermating of these RILs were investigated. QTL mapping made use of the previously constructed over 3300 cM linkage map of the RIL population. Three, five, two, two and six chromosome regions were identified, respectively, for their association with SPL, SPN, FSPN, SSPN, and compactness in at least two of the three environments examined. All compactness QTLs but one shared the respective intervals of QSpn.nau-5A and the SPL QTLs. Xcfd46–Xwmc702 interval on chromosome 7D was related to all traits but SSPN and had consistently the largest effects. The fact that not all the compactness QTL intervals were related to both SPL and SPN indicates that compactness is regulated by different mechanisms. Interval coincidence between QTLs of SPL and SPN and between QTLs of FSPN and SSPN was minimal. For all the traits, favorable alleles exist in both parents. Inheritance modes from additiveness to overdominance of the QTLs were revealed and two-locus interactions were detected, implying that the traits studied are under complex genetic control. The results could contribute to wheat yield improvement and better use of Wangshuibai and Nanda2419 the two special germplasms in wheat breeding program.

A jacalin-related lectin-like gene in wheat is a component of the plant defence system

Jacalin-related lectins (JRLs) are a subgroup of proteins with one or more jacalin-like lectin domains. Although JRLs are often associated with biotic or abiotic stimuli, their biological functions in plants, as well as their relationships to plant disease resistance, are poorly understood. A mannose-specific JRL (mJRL)-like gene (TaJRLL1) that is mainly expressed in stem and spike and encodes a protein with two jacalin-like lectin domains was identified in wheat. Pathogen infection and phytohormone treatments induced its expression; while application of the salicylic acid (SA) biosynthesis inhibitor paclobutrazol and the jasmonic acid (JA) biosynthesis inhibitor diethyldithiocarbamic acid, respectively, substantially inhibited its expression. Attenuating TaJRLL1 through virus-induced gene silencing increased susceptibility to the facultative fungal pathogen Fusarium graminearum and the biotrophic fungal pathogen Blumeria graminis. Arabidopsis thaliana transformed with TaJRLL1 displayed increased resistance to F. graminearum and Botrytis cinerea. JA and SA levels in transgenic Arabidopsis increased significantly. A loss or increase of disease resistance due to an alteration in TaJRLL1 function was correlated with attenuation or enhancement of the SA- and JA-dependent defence signalling pathways. These results suggest that TaJRLL1 could be a component of the SA- and JA-dependent defence signalling pathways.

Wheat Cryptochromes: Subcellular Localization and Involvement in Photomorphogenesis and Osmotic Stress Responses

Cryptochromes (CRYs) are blue light receptors important for plant growth and development. Comprehensive information on monocot CRYs is currently only available for rice (Oryza sativa). We report here the molecular and functional characterization of two CRY genes, TaCRY1a and TaCRY2, from the monocot wheat (Triticum aestivum). The expression of TaCRY1a was most abundant in seedling leaves and barely detected in roots and germinating embryos under normal growth conditions. The expression of TaCRY2 in germinating embryos was equivalent to that in leaves and much higher than the TaCRY1a counterpart. Transition from dark to light slightly affected the expression of TaCRY1a and TaCRY2 in leaves, and red light produced a stronger induction of TaCRY1a. Treatment of seedlings with high salt, polyethylene glycol, and abscisic acid (ABA) up-regulated TaCRY2 in roots and germinating embryos. TaCRY1a displays a light-responsive nucleocytoplasmic shuttling pattern similar to that of Arabidopsis (Arabidopsis thaliana) CRY1, contains nuclear localization domains in both the N and C termini, and includes information for nuclear export in its N-terminal domain. TaCRY2 was localized to the nucleus in the dark. Expression of TaCRY1a-green fluorescent protein or TaCRY2-green fluorescent protein in Arabidopsis conferred a shorter hypocotyl phenotype under blue light. These transgenic Arabidopsis plants showed higher sensitivity to high-salt, osmotic stress, and ABA treatment during germination and postgermination development, and they displayed altered expression of stress/ABA-responsive genes. The primary root growth in transgenic seedlings was less tolerant of ABA. These observations indicate that TaCRY1 and TaCRY2 might be involved in the ABA signaling pathway in addition to their role in primary blue light signal transduction.

Association of jacalin-related lectins with wheat responses to stresses revealed by transcriptional profiling

Jacalin-related lectins (JRLs) are carbohydrate-binding proteins widely present in plants and have one or more jacalin domains in common. However, JRLs’ structural types and functions are still poorly understood. In the present study, a total of 67 wheat (Triticum aestivum) JRL genes were identified through an exhausted search of EST database coupling with genome walking using published 454 sequence reads of Chinese Spring. A comparison of the translated wheat JRL proteins with those from other plants showed plant JRLs generally had low sequence similarity within and between species but exhibited conserved modular domain structures. More JRL genes encoded multiple jacalin domains in Arabidopsis thaliana, whereas more genes encoded chimeric JRLs in cereal plants. Dirigent domain-containing JRL genes were Poaceae-specific and accounted for nearly half of the identified wheat JRL genes. The dirigent domains were evolutionarily significantly correlated with the covalently linked jacalin domains. A phylogenetic analysis showed JRL proteins have experienced a substantial diversification after speciation. Moreover, new structural features conserved across the taxa were identified. Digital expression analysis and RT-PCR assays showed the expression of wheat JRL genes was largely tissue specific, typically low, and mostly inducible by biotic and abiotic stresses and stress hormones. These results suggest plant JRLs are critical for plant adaptation to stressful environments.

Mapping chromosomal regions affecting flowering time in a spring wheat RIL population

Flowering time is an important trait for the adaptation of wheat to its target environments. To identify chromosome regions associated with flowering time in wheat, a whole genome scan was conducted with five sets of field trial data on a recombinant inbred lines (RIL) population derived from the cross of spring wheat cultivars ‘Nanda 2419’ and ‘Wangshuibai’. The identified QTLs involved seven chromosomal regions, among which QFlt.nau-1B and QFlt.nau-2B were homoeologous to QFlt.nau-1D and QFlt.nau-2D, respectively. Nanda 2419, the earlier flowering parent, contributed early flowering alleles at five of these QTLs. QFlt.nau-1B and QFlt.nau-7B had the largest effects in all trials and were mapped to the Xwmc59.2–Xbarc80 interval on chromosome 1BS and the Xgwm537–Xgwm333 interval on 7BS. Most of the mapped QTL intervals were not coincident with known vernalization response or photoperiod sensitivity loci and QFlt.nau-1B seems to be an orthologue of EpsAm1. Four pairs of loci showed significant interactions across environments in determining flowering time, all of which involved QFlt.nau-1B. These findings are of significance to wheat breeding programs.

PmX: a recessive powdery mildew resistance gene at the Pm4 locus identified in wheat landrace Xiaohongpi.

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most devastating foliar diseases of wheat and imposes a constant challenge on wheat breeders. Xiaohongpi, a Chinese landrace of wheat (Triticum aestivum L.), shows resistance to powdery mildew during the entire growth stage in the field and under controlled conditions. The F1 plants from cross of the powdery mildew susceptible cultivar Yangmai158 with Xiaohongpi were susceptible to isolate Bgt19, the locally most prevalent Bgt isolate. In the derived F2 population and F3 progenies, the resistance segregation deviated significantly from the one-gene Mendelian ratio. However, marker analysis indicated that only one recessive gene conferred the resistance, which co-segregated with Xsts-bcd1231 that showed co-segregation with Pm4a in different studies. Allelism test indicated that this recessive resistance gene, designated as pmX, is either allelic or tightly linked to Pm4a. The pmX gene was different from Pm4 alleles in resistance spectrum. Examination of the genotype frequencies at pmX and the linked marker loci in the F2 population showed that a genetic variation favoring the transmission of Xiaohongpi alleles could be the cause of deviated segregation. Mapping of the pmX-linked markers using Chinese Spring deletion lines indicated that it resides in the 0.85–1.00 bin of chromosome 2AL.

Classification and expression diversification of wheat dehydrin genes.

Dehydrins (DHNs) are late embryonic abundant proteins characterized by the dehydrin domains that are involved in plant abiotic stress tolerance. In this study, fifty-four wheat DHN unigenes were identified in the expressed sequence tags database. These genes encode seven types of dehydrins (KS, SK3, YSK2, Y2SK2, Kn, Y2SK3, and YSK3) and separate in 32 homologous clusters. The gene amplification differed among the dehydrin types, and members of the YSK2- and Kn-type DHNs are more numerous in wheat than in other cereals. The relative expression of all of these DHN clusters was analyzed using an in silico method in seven tissue types (i.e. normal growing shoots, roots, and reproductive tissues; developing and germinating seeds; drought- and cold-stressed shoots) as well as semi-quantitative reverse transcription polymerase chain reaction in seedling leaves and roots treated by dehydration, cold, and salt, respectively. The role of the ABA pathway in wheat DHN expression regulation was analyzed. Transcripts of certain types of DHNs accumulated specifically according to tissue type and treatment, which suggests their differentiated roles in wheat abiotic stress tolerance.

Expression and responses to dehydration and salinity stresses of V-PPase gene members in wheat

Vacuolar H(+)-translocating pyrophosphatase (V-PPase) is a key enzyme related to plant growth as well as abiotic stress tolerance. In this work, wheat V-PPase genes TaVP1, TaVP2 and TaVP3 were identified. TaVP1 and TaVP2 are more similar to each other than to TaVP3. Their deduced polypeptide sequences preserve the topological structure and essential residues of V-PPases. Phylogenetic studies suggested that monocot plants, at least monocot grasses, have three VP paralogs. TaVP3 transcripts were only detected in developing seeds, and no TaVP2 transcripts were found in germinating seeds. TaVP2 was mainly expressed in shoot tissues and down-regulated in leaves under dehydration. Its expression was up-regulated in roots under high salinity. TaVP1 was relatively more ubiquitously and evenly expressed than TaVP2. Its expression level in roots was highest among the tissues examined, and was inducible by salinity stress. These results indicated that the V-PPase gene paralogs in wheat are differentially regulated spatially and in response to dehydration and salinity stresses.

Fine mapping TaFLW1, a major QTL controlling flag leaf width in bread wheat (Triticum aestivum L.)

AbstractIntroductionFlag leaf width (FLW) is directly related to photosynthetic capacity and yield potential in wheat. In a previous study, Qflw.nau-5A controlling FLW was detected on chromosome 5A in the interval possessing Fhb5 for type I Fusarium head blight (FHB) resistance using a recombinant inbred line population derived from Nanda2419 × Wangshuibai.Materials and methodsQflw.nau-5A near-isogenic line (NIL) with the background of Mianyang 99-323 and PH691 was developed and evaluated. FLW inheritance was investigated using two F2 populations developed from crossing the Qflw.nau-5A NILs with their recurrent parents. One hundred ten and 28 recombinants, which included 10 and 5 types of recombinants, were identified from 2816 F2 plants with Mianyang 99-323 background and 1277 F2 plants with PH691 background, respectively, and phenotyped in field trials for FLW and type I FHB resistance. Deletion bin mapping was applied to physically map Qflw.nau-5A.Results and conclusionsThe introduction of Wangshuibai Qflw.nau-5A allele reduced the FLW up to 3 mm. In the F2 populations, Qflw.nau-5A was inherited like a semi-dominant gene, and was therefore designated as TaFLW1. The FLW of the recombinant lines displayed a distinct two-peak distribution. Recombinants with wider leaves commonly have Mianyang 99-323 or PH691 chromatin in the 0.2 cM Xwmc492-Xwmc752 interval that resided in the 5AL12-0.35–0.57 deletion bin, and recombinants with narrow leaves were Wangshuibai genotype in this interval. Phenotypic recombination between FLW and type I FHB resistance was identified, implying TaFLW1 was in close linkage with Fhb5. These results should aid wheat breeders to break the linkage drag through marker-assisted selection and assist in the map-based cloning of TaFLW1.

Sequence variations of the partially dominant DELLA gene Rht-B1c in wheat and their functional impacts

Rht-B1c, allelic to the DELLA protein-encoding gene Rht-B1a, is a natural mutation documented in common wheat (Triticum aestivum). It confers variation to a number of traits related to cell and plant morphology, seed dormancy, and photosynthesis. The present study was conducted to examine the sequence variations of Rht-B1c and their functional impacts. The results showed that Rht-B1c was partially dominant or co-dominant for plant height, and exhibited an increased dwarfing effect. At the sequence level, Rht-B1c differed from Rht-B1a by one 2kb Veju retrotransposon insertion, three coding region single nucleotide polymorphisms (SNPs), one 197bp insertion, and four SNPs in the 1kb upstream sequence. Haplotype investigations, association analyses, transient expression assays, and expression profiling showed that the Veju insertion was primarily responsible for the extreme dwarfing effect. It was found that the Veju insertion changed processing of the Rht-B1c transcripts and resulted in DELLA motif primary structure disruption. Expression assays showed that Rht-B1c caused reduction of total Rht-1 transcript levels, and up-regulation of GATA-like transcription factors and genes positively regulated by these factors, suggesting that one way in which Rht-1 proteins affect plant growth and development is through GATA-like transcription factor regulation.