Transcriptome and biochemical analysis in hexaploid wheat with contrasting tolerance to iron deficiency pinpoints multi-layered molecular process.

Iron (Fe) is an essential plant nutrient that is indispensable for many physiological activities. This study is an effort to identify the molecular and biochemical basis of wheat genotypes with contrasting tolerance towards Fe deficiency. Our physiological experiments performed at the early growth stage in cv. Kanchan (KAN) showed Fe deficiency tolerance, whereas cv. PBW343 (PBW) was susceptible. Under Fe deficient condition, KAN showed delayed chlorosis, high SPAD values, and low malondialdehyde content compared to PBW, indicative of Fe deficient condition. Comparative shoot transcriptomics revealed increased expression of photosynthetic pathway genes in PBW, further suggesting its sensitivity to Fe fluctuations. Under Fe deficiency, both the cultivars showed distinct molecular re-arrangements such as high expression of genes involved in Fe uptake (including membrane transporters) and its remobilization. Specifically, in KAN these changes lead to high root phytosiderophores (PS) biosynthesis and its release, resulting in enhanced Fe translocation index. Utilizing the non-transgenic TILLING (Targeting Induced Lesions in Genomes) technology, we identified TaZIFL4.2D as a putative PS efflux transporter. Characterization of the wheat TILLING lines indicated that TaZIFL4.2 functions in PS release and Fe acquisition, thereby imparting tolerance to Fe deficiency. Altogether, this work highlights the mechanistic insight into Fe deficiency tolerance of hexaploid wheat, thus enabling breeders to select suitable genotypes to utilize nutrients for maximum yields.

Comparative analysis of VMT genes/proteins in selected plant species with emphasis on bread wheat (Triticum aestivum L.).

BACKGROUND: In recent years, the study of molecular basis of uptake, transport and utilization of grain Fe/Zn (GFe/GZn) in wheat has been an active area of research. As a result, it has been shown that a number of transporters are involved in uptake and transport of Fe. In a recent study, knockout of a transporter gene OsVMT (VACUOLAR MUGINEIC ACID TRANSPORTER) in rice was shown to be involved in Fe homoeostasis. OBJECTIVE: In this study, we analysed VMT genes among six monocots and three dicots with major emphasis on wheat VMT genes (TaVMTs), taking OsVMT gene as a reference. METHODS AND RESULTS: Using OsVMT gene as a reference, VMT genes were identified and sequence similarities were examined among six monocots and three dicots. Each VMT protein carried one functional domain and 7 to 10 distinct motifs (including 9 novel motifs). The qRT-PCR analysis showed differential expression by all the six TaVMT genes in pairs of contrasting wheat genotypes with high (FAR4 and WB02) and low (K8027 and HD3226) GFe/GZn at two different grain filling stages (14 DAA and 28 DAA). TaVMT1 genes showed up-regulation in high GFe/Zn genotypes relative to low GFe/Zn genotypes, whereas the TaVMT2 genes showed down-regulation or nonsignificant up-regulation in a few cases. CONCLUSIONS: At 14 DAA, each of the six TaVMT genes exhibited higher expression in wheat genotypes with high GFe and GZn relative to those with low GFe and GZn, suggesting major role of VMT genes in improvement of grain Fe/Zn homoeostasis, thus making TaVMT genes useful for improvement in Fe/Zn in wheat grains.

Genome sequencing and assembly of Lathyrus sativus - a nutrient-rich hardy legume crop.

Grass pea (Lathyrus sativus) is a cool-season legume crop tolerant to drought, salinity, waterlogging, insects, and other biotic stresses. Despite these beneficial traits, this crop is not cultivated widely due to the accumulation of a neurotoxin - ß-N-oxalyl-L-α, ß-diaminopropionic acid (ß-ODAP) in the seeds and its association with neurolathyrism. In this study, we sequenced and assembled the genome of Lathyrus sativus cultivar Pusa-24, an elite Indian cultivar extensively used in breeding programs. The assembled genome of Lathyrus was 3.80 Gb in length, with a scaffold N50 of 421.39 Mb. BUSCO assessment indicated that 98.3% of highly conserved Viridiplantae genes were present in the assembly. A total of 3.17 Gb (83.31%) of repetitive sequences and 50,106 protein-coding genes were identified in the Lathyrus assembly. The Lathyrus genome assembly reported here thus provides a much-needed and robust foundation for various genetic and genomic studies in this vital legume crop.

Unraveling novel and rare mutations for alpha-amylase and key transcription factors in EMS-induced wheat mutants for amylose by TILLING.

BACKGROUND: TILLING (Targeting Induced Local Lesions in Genomes) is a reverse-genetic strategy that is used to locate an allelic series of induced point mutations in genes of interest. High-throughput TILLING allows the rapid and cost-effective detection of induced point mutations in populations of chemically mutagenized individuals. Grain amylose content is the major constraints for its nutritional quality and have drawn research interest. Identification of allelic variations in genes involved in starch biosynthesis in wheat endosperm is pre-requisite to amenable for nutritional quality improvement. METHODS AND RESULTS: In this study, 44 EMS-induced (M4 generation) mutant lines having variation for amylose content were used for TILLING sequencing. Overall 2098.08 kb of the sequence was analyzed, and the average mutation density was 1/65.56 kb. In analysis, at the high depth score a total of 32 variations were identified including three natural variations, 76% transitions, 10% transversions, and 14% InDels respectively. The substitutions led to intronic variants, UTRs and up-downstream gene variants in Alpha-amylase, TabZIP77.1, TabZIP1 and Myb respectively. In the Myb transcription factor two missense mutations recorded namely Myb_7B c.680G > A and c.1358 T > C led to p.Gly227Asp and p.Met453Thr and c.1390G > A one substitution in Myb_7D led to p.Val464Ile. CONCLUSION: The identified missense substitutions were predicted to affect the protein function; hence they may have a probable role in context to the amylose content in mutants. The mutations ascertained in the current study will help in gene discovery in wheat and identified mutants can be used as genetic resources to improve nutritional quality of wheat.

Effect of debranning on grains and meal characteristics of different Indian and exotic wheat varieties.

The objective of this work was to evaluated the effects of debranning (2% and 4%) of Indian and exotic wheat varieties on pasting, protein profile and rheological properties of meal. Exotic varieties grains showed significant difference in cooking properties despite having similar protein content. Debranned grains of exotic varieties showed significantly lower water uptake (WU) than those from Indian varieties. Ash content, protein content and mixographic properties (mixing time, dough strength) of meal decreased with increase in extent of debranning. With increase in debranning level unextractable polymeric proteins (UnEx-PP) decreased while unextractable monomeric proteins (UnEx-MP) increased. Exotic varieties had lower extractable PP as compared to Indian wheat varieties. With increase in debranning level pasting parameters (final, breakdown and peak viscosity) increased. Exotic varieties showed the higher gluten strength indicated by mixographic parameters. Wheat grains debranned to 4% debranning level showed better cooking properties. Exotic wheat varieties showed better pasting and mixing properties as compared to Indian wheat varieties.

Trait Mapping Approaches Through Association Analysis in Plants.

Previously, association mapping (AM) methodology was used to unravel genetic complications in animal science by measuring the complex traits for candidate and non-candidate genes. Nowadays, this statistical approach is widely used to clarify the complexity in plant breeding program-based genome-wide breeding strategies, marker development, and diversity analysis. This chapter is particularly focused on methodologies with limitations and provides an overview of AM models and software used up to now. Association or linkage disequilibrium mapping has become a very popular method for discovering candidate and non-candidate genes and confirmation of quantitative trait loci (QTL) on various parts of the genome and in marker-assisted selection for breeding. Previously, various QTL investigations were carried out for different plants exclusively by linkage mapping. To help to understand the basics of modern molecular genetic techniques, in this chapter we summarize previous studies done on different crops. AM offers high-resolution power when there is large genotypic diversity and low linkage disequilibrium (LD) for the germplasm being investigated. The benefits of AM, compared with traditional QTL mapping, include a relatively detailed mapping resolution and a far less time-consuming approach since no mapping populations need to be generated. The advancements in genotyping and computational techniques have encouraged the use of AM. AM provides a fascinating approach for genetic investigation of QTLs, due to its resolution and the possibility to study the various genomic areas at the same time without construction of mapping populations. In this chapter we also discuss the advantages and disadvantages of AM, especially in the dicotyledonous crops Fabaceae and Solanaceae, with various genome-size reproductive strategies (clonal vs. sexual), and statistical models. The main objective of this chapter is to highlight the uses of association genetics in major and minor crop species that have trouble being analyzed for dissection of complex traits by identification of the factor responsible for controlling the effect of trait. Graphical Abstract.

Cotton leaf curl Burewala virus with intact or mutant transcriptional activator proteins: complexity of cotton leaf curl disease.

Cotton leaf curl disease (CLCuD) is a serious disease of cotton on the Indian subcontinent. In the present study, three cotton leaf curl viruses, cotton leaf curl Burewala virus (CLCuBuV), cotton leaf curl Kokhran virus (CLCuKoV) and cotton leaf curl Multan virus (CLCuMV), and their associated satellites, cotton leaf curl Multan betasatellite (CLCuMB) and cotton leaf curl Multan alphasatellite (CLCuMA), were detected. CLCuBuV with either intact (CLCuBuV-1) or mutant (CLCuBuV-2) transcriptional activator protein (TrAP) were detected in different plants. Agroinoculation with CLCuBuV-1 or CLCuBuV-2 together with CLCuMB and CLCuMA, resulted in typical leaf curling and stunting of tobacco plants. Inoculation with CLCuKoV or an isolate of CLCuMV (CLCuMV-2), together with CLCuMB and CLCuMA, induced severe leaf curling, while the other isolate of CLCuMV (CLCuMV-1), which was recombinant in origin, showed mild leaf curling in tobacco. To investigate the effect of intact or mutant TrAP and also the recombination events, CLCuBuV-1, CLCuBuV-2, CLCuMV-1 or CLCuMV-2 together with the satellites (CLCuMA and CLCuMB) were transferred to cotton via whitefly-mediated transmission. Cotton plants containing CLCuBuV-1, CLCuBuV-2 or CLCuMV-2 together with satellites showed curling and stunting, whereas the plants having CLCuMV-1 and the satellites showed only mild and indistinguishable symptoms. CLCuBuV-1 (intact TrAP) showed severe symptoms in comparison to CLCuBuV-2 (mutant TrAP). The present study reveals that two types of CLCuBuV, one with an intact TrAP and the other with a mutant TrAP, exist in natural infection of cotton in India. Additionally, CLCuMuV-1, which has a recombinant origin, induces mild symptoms in comparison to the other CLCuMV isolates.

Differential expression of structural genes for the late phase of phytic acid biosynthesis in developing seeds of wheat (Triticum aestivum L.).

In cereals, phytic acid (PA) or inositol hexakisphosphate (IP6) is a well-known phosphate storage compound as well as major chelator of important micronutrients (iron, zinc, calcium, etc.). Genes involved in the late phases of PA biosynthesis pathway are known in crops like maize, soybeans and barley but none have been reported from wheat. Our in silico analysis identified six wheat genes that might be involved in the biosynthesis of inositol phosphates. Four of the genes were inositol tetraphosphate kinases (TaITPK1, TaITPK2, TaITPK3, and TaITPK4), and the other two genes encode for inositol triphosphate kinase (TaIPK2) and inositol pentakisphosphate kinase (TaIPK1). Additionally, we identified a homolog of Zmlpa-1, an ABCC subclass multidrug resistance-associated transporter protein (TaMRP3) that is putatively involved in PA transport. Analyses of the mRNA expression levels of these seven genes showed that they are differentially expressed during seed development, and that some are preferentially expressed in aleurone tissue. These results suggest selective roles during PA biosynthesis, and that both lipid-independent and -dependent pathways are active in developing wheat grains. TaIPK1 and TaMRP3 were able to complement the yeast ScΔipk1 and ScΔycf1 mutants, respectively, providing evidence that the wheat genes have the expected biochemical functions. This is the first comprehensive study of the wheat genes involved in the late phase of PA biosynthesis. Knowledge generated from these studies could be utilized to develop strategies for generating low phyate wheat.

Association mapping of spot blotch resistance in wild barley.

Spot blotch, caused by Cochliobolus sativus, is an important foliar disease of barley. The disease has been controlled for over 40 years through the deployment of cultivars with durable resistance derived from the line NDB112. Pathotypes of C. sativus with virulence for the NDB112 resistance have been detected in Canada; thus, many commercial cultivars are vulnerable to spot blotch epidemics. To increase the diversity of spot blotch resistance in cultivated barley, we evaluated 318 diverse wild barley accessions comprising the Wild Barley Diversity Collection (WBDC) for reaction to C. sativus at the seedling stage and utilized an association mapping (AM) approach to identify and map resistance loci. A high frequency of resistance was found in the WBDC as 95% (302/318) of the accessions exhibited low infection responses. The WBDC was genotyped with 558 Diversity Array Technology (DArT((R))) and 2,878 single nucleotide polymorphism (SNP) markers and subjected to structure analysis before running the AM procedure. Thirteen QTL for spot blotch resistance were identified with DArT and SNP markers. These QTL were found on chromosomes 1H, 2H, 3H, 5H, and 7H and explained from 2.3 to 3.9% of the phenotypic variance. Nearly half of the identified QTL mapped to chromosome bins where spot blotch resistance loci were previously reported, offering some validation for the AM approach. The other QTL mapped to unique genomic regions and may represent new spot blotch resistance loci. This study demonstrates that AM is an effective technique for identifying and mapping QTL for disease resistance in a wild crop progenitor. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11032-010-9402-8) contains supplementary material, which is available to authorized users.