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A well-known physiological adaptation process of plants encountering drying soil is to achieve water balance by reducing shoot growth and maintaining or promoting root elongation, but little is known about the molecular basis of this process. This study investigated the role of a drought-up-regulated Triticum aestivum NAC69-1 (TaNAC69-1) in the modulation of root growth in wheat. TaNAC69-1 was predominantly expressed in wheat roots at the early vegetative stage. Overexpression of TaNAC69-1 in wheat roots using OsRSP3 (essentially root-specific) and OsPIP2;3 (root-predominant) promoters resulted in enhanced primary seminal root length and a marked increase in maturity root biomass. Competitive growth analysis under water-limited conditions showed that OsRSP3 promoter-driven TaNAC69-1 transgenic lines produced 32% and 35% more above-ground biomass and grains than wild-type plants, respectively. TaNAC69-1 overexpression in the roots down-regulated the expression of TaSHY2 and TaIAA7, which are from the auxin/IAA (Aux/IAA) transcriptional repressor gene family and are the homologs of negative root growth regulators SHY2/IAA3 and IAA7 in Arabidopsis. The expression of TaSHY2 and TaIAA7 in roots was downregulated by drought stress and up-regulated by cytokinin treatment, which inhibited root growth. DNA binding and transient expression analyses revealed that TaNAC69-1 bound to the promoters of TaSHY2 and TaIAA7, acted as a transcriptional repressor and repressed the expression of reporter genes driven by the TaSHY2 or TaIAA7 promoter. These data suggest that TaNAC69-1 is a transcriptional repressor of TaSHY2 and TaIAA7 homologous to Arabidopsis negative root growth regulators and is likely to be involved in promoting root elongation in drying soil. [ABSTRACT FROM AUTHOR]

• Background Cereal diseases cause tens of billions of dollars of losses annually and have devastating humanitarian consequences in the developing world. Increased understanding of the molecular basis of cereal host-pathogen interactions should facilitate development of novel resistance strategies. However, achieving this in most cereals can be challenging due to large and complex genomes, long generation times and large plant size, as well as quarantine and intellectual property issues that may constrain the development and use of community resources. Brachypodium distachyon (brachypodium) with its small, diploid and sequenced genome, short generation time, high transformability and rapidly expanding community resources is emerging as a tractable cereal model. • Scope Recent research reviewed here has demonstrated that brachypodium is either susceptible or partially susceptible to many of the major cereal pathogens. Thus, the study of brachypodium-pathogen interactions appears to hold great potential to improve understanding of cereal disease resistance, and to guide approaches to enhance this resistance. This paper reviews brachypodium experimental pathosystems for the study of fungal, bacterial and viral cereal pathogens; the current status of the use of brachypodium for functional analysis of cereal disease resistance; and comparative genomic approaches undertaken using brachypodium to assist characterization of cereal resistance genes. Additionally, it explores future prospects for brachypodium as a model to study cereal-pathogen interactions. • Conclusions The study of brachypodium-pathogen interactions appears to be a productive strategy for understanding mechanisms of disease resistance in cereal species. Knowledge obtained from this model interaction has strong potential to be exploited for crop improvement. [ABSTRACT FROM AUTHOR]

A wheat HsfA6 member acts as a transcriptional activator for up-regulation of a suite of heat stress protection genes including previously unknown Hsf targets such as Golgi anti-apoptotic protein.Heat stress is a significant environmental factor adversely affecting crop yield. Crop adaptation to high-temperature environments requires transcriptional reprogramming of a suite of genes involved in heat stress protection. This study investigated the role of TaHsfA6f, a member of the A6 subclass of heat shock transcription factors, in the regulation of heat stress protection genes in Triticum aestivum (bread wheat), a poorly understood phenomenon in this crop species. Expression analysis showed that TaHsfA6f was expressed constitutively in green organs but was markedly up-regulated during heat stress. Overexpression of TaHsfA6f in transgenic wheat using a drought-inducible promoter resulted in up-regulation of heat shock proteins (HSPs) and a number of other heat stress protection genes that included some previously unknown Hsf target genes such as Golgi anti-apoptotic protein (GAAP) and the large isoform of Rubisco activase. Transgenic wheat plants overexpressing TaHsfA6f showed improved thermotolerance. Transactivation assays showed that TaHsfA6f activated the expression of reporter genes driven by the promoters of several HSP genes (TaHSP16.8, TaHSP17, TaHSP17.3, and TaHSP90.1-A1) as well as TaGAAP and TaRof1 (a co-chaperone) under non-stress conditions. DNA binding analysis revealed the presence of high-affinity TaHsfA6f-binding heat shock element-like motifs in the promoters of these six genes. Promoter truncation and mutagenesis analyses identified TaHsfA6f-binding elements that were responsible for transactivation of TaHSP90.1-A1 and TaGAAP by TaHsfA6f. These data suggest that TaHsfA6f is a transcriptional activator that directly regulates TaHSP, TaGAAP, and TaRof1 genes in wheat and its gene regulatory network has a positive impact on thermotolerance. [ABSTRACT FROM AUTHOR]

Heat shock factors (Hsfs) play a central regulatory role in acquired thermotolerance. To understand the role of the major molecular players in wheat adaptation to heat stress, the Hsf family was investigated in Triticum aestivum. Bioinformatic and phylogenetic analyses identified 56 TaHsf members, which are classified into A, B, and C classes. Many TaHsfs were constitutively expressed. Subclass A6 members were predominantly expressed in the endosperm under non-stress conditions. Upon heat stress, the transcript levels of A2 and A6 members became the dominant Hsfs, suggesting an important regulatory role during heat stress. Many TaHsfA members as well as B1, C1, and C2 members were also up-regulated during drought and salt stresses. The heat-induced expression profiles of many heat shock protein (Hsp) genes were paralleled by those of A2 and A6 members. Transactivation analysis revealed that in addition to TaHsfA members (A2b and A4e), overexpression of TaHsfC2a activated expression of TaHsp promoter-driven reporter genes under non-stress conditions, while TaHsfB1b and TaHsfC1b did not. Functional heat shock elements (HSEs) interacting with TaHsfA2b were identified in four TaHsp promoters. Promoter mutagenesis analysis demonstrated that an atypical HSE (GAACATTTTGGAA) in the TaHsp17 promoter is functional for heat-inducible expression and transactivation by Hsf proteins. The transactivation of Hsp promoter-driven reporter genes by TaHsfC2a also relied on the presence of HSE. An activation motif in the C-terminal domain of TaHsfC2a was identified by amino residue substitution analysis. These data demonstrate the role of HsfA and HsfC2 in regulation of Hsp genes in wheat. [ABSTRACT FROM PUBLISHER]

Fructans are the major component of temporary carbon reserve in the stem of temperate cereals, which is used for grain filling. Three families of fructosyltransferases are directly involved in fructan synthesis in the vacuole of Triticum aestivum. The regulatory network of the fructan synthetic pathway is largely unknown. Recently, a sucrose-upregulated wheat MYB transcription factor (TaMYB13-1) was shown to be capable of activating the promoter activities of sucrose:sucrose 1-fructosyltransferase (1-SST) and sucrose:fructan 6-fructosyltransferase (6-SFT) in transient transactivation assays. This work investigated TaMYB13-1 target genes and their influence on fructan synthesis in transgenic wheat. TaMYB13-1 overexpression resulted in upregulation of all three families of fructosyltransferases including fructan:fructan 1-fructosyltransferase (1-FFT). A γ-vacuolar processing enzyme (γ-VPE1), potentially involved in processing the maturation of fructosyltransferases in the vacuole, was also upregulated by TaMYB13-1 overexpression. Multiple TaMYB13 DNA-binding motifs were identified in the Ta1-FFT1 and Taγ-VPE1 promoters and were bound strongly by TaMYB13-1. The expression profiles of these target genes and TaMYB13-1 were highly correlated in recombinant inbred lines and during stem development as well as the transgenic and non-transgenic wheat dataset, further supporting a direct regulation of these genes by TaMYB13-1. TaMYB13-1 overexpression in wheat led to enhanced fructan accumulation in the leaves and stems and also increased spike weight and grain weight per spike in transgenic plants under water-limited conditions. These data suggest that TaMYB13-1 plays an important role in coordinated upregulation of genes necessary for fructan synthesis and can be used as a molecular tool to improve the high fructan trait. [ABSTRACT FROM AUTHOR]

NAC proteins are plant-specific transcription factors and enriched with members involved in plant response to drought stress. In this study, we analyzed the expression profiles of TaNAC69 in bread wheat using Affymetrix Wheat Genome Array datasets and quantitative RT–PCR. TaNAC69 expression was positively associated with wheat responses to both abiotic and biotic stresses and was closely correlated with a number of stress up-regulated genes. The functional analyses of TaNAC69 in transgenic wheat showed that TaNAC69 driven by a barley drought-inducible HvDhn4s promoter led to marked drought-inducible overexpression of TaNAC69 in the leaves and roots of transgenic lines. The HvDhn4s:TaNAC69 transgenic lines produced more shoot biomass under combined mild salt stress and water-limitation conditions, had longer root and more root biomass under polyethylene glycol-induced dehydration. Analysis of transgenic lines with constitutive overexpression of TaNAC69 showed the enhanced expression levels of several stress up-regulated genes. DNA-binding assays revealed that TaNAC69 and its rice homolog (ONAC131) were capable of binding to the promoter elements of three rice genes (chitinase, ZIM, and glyoxalase I) and an Arabidopsis glyoxalase I family gene, which are homologs of TaNAC69 up-regulated stress genes. These data suggest that TaNAC69 is involved in regulating stress up-regulated genes and wheat adaptation to drought stress. [ABSTRACT FROM PUBLISHER]

Water-soluble carbohydrates (WSCs; composed of mamly fructans, sucrose [Suc], glucose [Gic], and fructose) deposited in wheat (Triticum aestivum) stems are important carbon sources for grain filling. Variation in stem WSC concentrations among wheat genotypes is one of the genetic factors influencing grain weight and yield under water-limited environments. Here, we describe the molecular dissection of carbohydrate metabolism in stems, at the WSC accumulation phase, of recombinant inbred Seri/Babax lines of wheat differing in stem WSC concentrations. Affymetrix GeneChip analysis of carbohydrate metabolic enzymes revealed that the mRNA levels of two fructan synthetic enzyme families (Suc:Suc 1-fructosyltransferase and Suc:fructan 6-fructosyltransferase) in the stem were positively correlated with stem WSC and fructan concentrations, whereas the mRNA levels of enzyme families involved in Suc hydrolysis (Suc synthase and soluble acid invertase) were inversely correlated with WSC concentrations. Differential regulation of the mRNA levels of these Suc hydrolytic enzymes in Seri/Babax lines resulted in genotypic differences in these enzyme activities. Down-regulation of Suc synthase and soluble acid. invertase in high WSC lines was accompanied by significant decreases in the mRNA levels of enzyme families related to sugar catabolic pathways (fructokinase and mitochondrion pyruvate dehydrogenase complex) and enzyme families involved in diverting UDP-Glc to cell wall synthesis (UDP-Glc 6-dehydrogenase, UDP-glucuronate decarboxylase, and cellulose synthase), resulting in a reduction in cell wall polysaccharide contents (mainly hemicellulose) in the stem of high WSC lines. These data suggest that differential carbon partitioning in the wheat stem is one mechanism that contributes to genotypic variation in WSC accumulation. [ABSTRACT FROM AUTHOR]