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Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a global threat to wheat production. Aegilops tauschii, one of the wheat progenitors, carries the YrAS2388 locus for resistance to Pst on chromosome 4DS. We reveal that YrAS2388 encodes a typical nucleotide oligomerization domain-like receptor (NLR). The Pst-resistant allele YrAS2388R has duplicated 3' untranslated regions and is characterized by alternative splicing in the nucleotide-binding domain. Mutation of the YrAS2388R allele disrupts its resistance to Pst in synthetic hexaploid wheat; transgenic plants with YrAS2388R show resistance to eleven Pst races in common wheat and one race of P. striiformis f. sp. hordei in barley. The YrAS2388R allele occurs only in Ae. tauschii and the Ae. tauschii-derived synthetic wheat; it is absent in 100% (n = 461) of common wheat lines tested. The cloning of YrAS2388R will facilitate breeding for stripe rust resistance in wheat and other Triticeae species.

It is known that both the number and the structure of somatic chromosomes can vary in early generation hexaploid wheats. The phenomenon is generally assumed to arise as a result of the meiotic instability characteristic of freshly created allopolyploids. Here, an analysis of the somatic karyotype of a set of 33 early generation synthetic hexaploid wheats has revealed that variation, taking the form of sub-chromosomal fragments and inter-chromosomal translocations, can also arise in somatic tissue. A possible explanation for the observations was that karyotypic instability in early generation hexaploid wheat probably occurs not just during sporogenesis, but also in somatic tissue. However, other factors such as the use of nitrous oxide during the experiments could also cause the chromosome variations, and additional experimentation would be required to determine the most likely. Key words: chromosomal variation, genome instability, somatic cell, synthetic wheat. Résumé : Il est bien connu que tant le nombre que la structure des chromosomes somatiques peuvent varier chez les blés hexaploïdes récemment synthétisés. Ce phénomène est généralement attribué à une instabilité méiotique chez les allopolyploïdes nouvellement créés. Dans ce travail, les auteurs réalisent une analyse du caryotype somatique chez 33 blés hexaploïdes récemment synthétisés et celle-ci révèle que des fragments sub-chromosomiques et des translocations inter-chromosomiques peuvent également survenir dans les tissus somatiques. Cependant, d'autres facteurs tels que l'utilisation de l'oxyde nitreux au cours de l'expérience pourraient aussi avoir causé ces variations chromosomiques et des expériences additionnelles seront nécessaires pour élucider cette incertitude. [Traduit par la Rédaction] Mots-clés : variation chromosomique, instabilité génomique, cellule somatique, blé synthétique., Introduction Allopolyploidy--the merging of two non-homologous genomes into a single nucleus achieved via a wide hybridization event--has provided an important route for plants to speciate and evolve. It has long [...]

Aegilops comosa and Ae. markgrafii are diploid progenitors of polyploidy species of Aegilops sharing M and C genomes, respectively. Transferring valuable genes/traits from Aegilops into wheat is an alternative strategy for wheat genetic improvement. The amphidiploids between diploid species of Aegilops and tetraploid wheat can act as bridges to overcome obstacles from direct hybridization and can be developed by the union of unreduced gametes. In this study, we developed seven Triticum turgidum - Ae. comosa and two T. turgidum - Ae. markgrafii amphidiploids. The unreduced gametes mechanisms, including first-division restitution (FDR) and single-division meiosis (SDM), were observed in triploid F1 hybrids of T. turgidum - Ae. comosa (STM) and T. turgidum - Ae. markgrafii (STC). Only FDR was observedinSTC hybrids, whereas FDRorboth FDR and SDM were detectedin the STM hybrids. All seven pairs of M chromosomes of Ae. comosa and C chromosomes of Ae. markgrafii were distinguished by fluorescent in situ hybridization (FISH) probes pSc119.2 and pTa71 combinations with pTa-535 and (CTT)12/(ACT)7, respectively. Meanwhile, the chromosomes of tetraploid wheat and diploid Aegilops parents were distinguished by the same FISH probes. The amphidiploids possessed specific valuable traits such as multiple tillers, large seed size related traits, and stripe rust resistance that could be utilized in the genetic improvement of wheat. Key words: Aegilops, amphidiploids, fluorescent in situ hybridization, unreduced gametes, C and M genomes. L'Aegilops comosa et l'Ae. markgrafii sont des especes diploides qui ont contribue les genomes M et C, respectivement, chez les especes polyploides d'Aegilops. Le transfert de caracteres ou de genes d'interet de l'Aegilops vers le ble constitue une approche alternative pour l'amelioration genetique du ble. Les amphidiploides entre des especes diploides du genre Aegilops et le ble tetraploide peuvent servir de ponts pour surmonter les obstacles rencontres lors de l'hybridation directe et on peut les produire par union de gametes non-reduits. Dans ce travail, les auteurs ont produit sept amphidiploides Triticum turgidum - Ae. comosa et deux amphidiploides T. turgidum - Ae. markgrafii. Les deux mecanismes menant a la production de gametes non-reduits, la restitution a la premiere division (FDR) et la meiose a une seule division (SDM), ont tous deux etes observes chez les hybrides F1 triploides T. turgidum - Ae. comosa (STM) et T. turgidum - Ae. margrafii (STC). Seul le FDR a ete observe au sein des hybrides STC, tandis que le FDR et le SDM ont tous deux etes detectes chez les hybrides STM. Les sept paires de chromosomes M de l'Ae. comosa et de chromosomes C de l'Ae. margrafii ont ete distingues en hybridation in situ en fluorescence (FISH) a l'aide des sondes pSc119.2 et pTa71 combinees avec les sondes pTa-535 et (CTT)12/(ACT)7, respectivement. En meme temps, les chromosomes parentaux du ble tetraploide et des Aegilops ont ete distingues au moyen des memes sondes FISH. Les amphidiploides presentaient des caracteres specifiques souhaites tels que de multiples talles, de gros grains et une resistance a la rouille striee qui seraient utiles en amelioration genetique du ble. [Traduit par la Redaction] Mots-cles : Aegilops, amphidiploides, hybridation in situ en fluorescence, gametes non-reduits, genomes C et M., Introduction Aegilops comosa and Ae. markgrafii are diploid donor species of polyploid Aegilops harboring the M and C genomes. These species possess genes/traits such as resistance to wheat stripe rust, [...]

Leaf rolling is regarded as an important morphological trait in wheat breeding. Moderate leaf rolling is helpful to keep leaves upright and improve the photosynthesis of plants, leading to increased yield. However, studies on the identification of genomic regions/genes associated with rolling leaf have been reported less frequently in wheat. In this study, a rolling leaf mutant, T73, which has paired spikelets, dwarfism, and delayed heading traits, was obtained from a common wheat landrace through ethyl methanesulfonate mutagenesis. The rlT73 mutation caused an increase in the number of epidermal cells on the abaxial side and the shrinkage of bulliform cells on the adaxial side, leading to an adaxially rolling leaf phenotype. Genetic analysis showed that the rolling leaf phenotype was controlled by a single recessive gene. Further Wheat55K single nucleotide polymorphism array-based bulked segregant analysis and molecular marker mapping delimited rlT73 to a physical interval of 300.29–318.33 Mb on the chromosome arm 1BL in the Chinese Spring genome. We show that a point mutation at the miRNA165/166 binding site of the HD zipper class III transcription factor on 1BL altered its transcriptional level, which may be responsible for the rolling leaf phenotype. Our results suggest the important role of rlT73 in regulating wheat leaf development and the potential of miRNA-based gene regulation for crop trait improvement. [ABSTRACT FROM AUTHOR]

The spikelet number per spike (SNS) and spike length (SL) are key traits of interest for improving grain yields. Photoperiod-1 (Ppd-1) is a key regulator of inflorescence architecture and paired spikelet development in wheat. In this study, 170 recombinant inbred lines (RILs) derived by crossing synthetic hexaploid wheat (SHW-L1) with a commercial cultivar (Chuanmai 32) were evaluated for the number of days to heading (DTH), SNS and SL in four different years. Eight PPD1 combination homoeologs were also identified in the RILs by using genetic marker analysis. DTH had highly significant or significant positive correlations with SNS and SL, while SL also had a highly significant positive correlation with SNS. As a single factor, the photoperiod-sensitive ppd-D1b alleles had the largest effect on delaying heading, and these results showed that SL and SNS can eventually be increased. These findings confirmed that photoperiod-sensitive ppd-D1b is a potential means of increasing wheat yields. [ABSTRACT FROM AUTHOR]