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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. [ABSTRACT FROM AUTHOR]

Plant U‐box (PUB) E3 ubiquitin ligases play essential roles in response to environmental stresses and hormone signaling, but little is known about them in wheat (Triticum aestivum L.). We characterized a U‐box E3 ubiquitin ligase gene, TaPUB15, which is conserved in wheat cultivars. TaPUB15 was expressed in multiple tissues, and the expression was much higher in roots than in other tissues. Transcription of TaPUB15 was induced by salt, abscisic acid, 4°C, and polyethylene glycol (PEG). Overexpression of TaPUB15‐D led to improve salt tolerance in transgenic rice, along with more roots in transgenic rice. Ion flux assays showed that transgenic rice plants had improved salt tolerance and maintained low Na+/K+ ratios under salinity stress. Gene expression assays indicated that several salt stress‐related genes were significantly upregulated in transgenic rice relative to the wild type. These results from transgenic rice were also verified in transgenic Arabidopsis. Our data showed that TaPUB15 plays crucial roles in enhancing salt tolerance in crop plants and served a valuable gene resource for promoting the breeding of salt‐tolerant wheat in the future. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]