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Open Access Publications from the University of California

Scholarly Works (30 results)

  • Article
  • Peer Reviewed
UC Riverside Previously Published Works (2017)
    Cover page: A set of new 1RS translocations from wheat cv. Amigo in a uniform genetic background
    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2017)

    Key message

    Engineered chromosomes 1BS and 1RS offer a new alternative in the development of hybrid systems in bread wheat and triticale. In the cytoplasmic male sterility system for hybrid wheat based on the cytoplasm of Triticum timopheevi fertility restoration is difficult, with few good restorer genes available. In the system based on the cytoplasms of Aegilops kotschyi, Ae. uniaristata and Ae. mutica, essentially all chromosomes 1B carry locus Rf multi that restores male fertility; male sterility manifests itself in wheats with the 1RS.1BL translocation where 1BS chromosome arm is missing. To generate male sterile wheats without the 1RS.1BL translocation, the 1BS arm was cytogenetically engineered to replace the segment with Rf multi with two short inserts of rye chromatin. Conversely, to enhance fertility restoration by doubling the number of restorers present for eventual use in wheat and triticale, a region of 1BS with Rf multi was inserted into 1RS. Alloplasmic wheats with Rf multi removed were completely male sterile; alloplasmic wheats with engineered 1RS carrying Rf multi and without normal 1B were male fertile. An exception to the ubiquitous presence of Rf multi is T. spelta var. duhamelianum; four accessions tested in this study gave inconsistent results but some did not restore male fertility. Engineered chromosomes 1BS and 1RS and chromosomes 1B of T. spelta offer a new alternative for practical application of a cytoplasmic male sterility system in the development of hybrid wheat and hexaploid triticale.
      Cover page: Chromosomes 1BS and 1RS for control of male fertility in wheats and triticales with cytoplasms of Aegilops kotschyi, Ae. mutica and Ae. uniaristata
      • Article
      • Peer Reviewed
      UC Riverside Previously Published Works (2022)
      In first division restitution (FDR)-type meiosis, univalents congregate on the metaphase I plate and separate sister chromatids in an orderly fashion, producing dyads with somatic chromosome numbers. The second meiotic division is abandoned. The separation of sister chromatids requires separation of otherwise fused sister centromeres and a bipolar attachment to the karyokinetic spindle. This study analyzed packaging of sister centromeres in pollen mother cells (PMCs) in a wheat-rye F1 hybrid with a mixture of standard reductional meiosis and FDR. No indication of sister centromere separation before MI was observed; such separation was clearly only visible in univalents placed on the metaphase plate itself, and only in PMCs undergoing FDR. Even in the FDR, PMCs univalents off the plate retained fused centromeres. Both the orientation and configuration of univalents suggest that some mechanism other than standard interactions with the karyokinetic spindle may be responsible for placing univalents on the plate, at which point sister centromeres are separated and normal amphitelic interaction with the spindle is established. At this point it is not clear at all what univalent delivery mechanism may be at play in the FDR.
        Cover page: Behavior of Centromeres during Restitution of the First Meiotic Division in a Wheat–Rye Hybrid
        • Article
        • Peer Reviewed
        UC Riverside Previously Published Works (2019)
        For normal transition through meiosis, chromosomes rely on pairing with their homologues. Chromosomes which fail to pair, univalents, behave irregularly and may undergo various types of breakage across their centromeres. Here, we analyzed the meiotic behavior of misdivision products themselves: isochromosomes and telocentrics in wheat. Both types of chromosomes behaved in the same fashion as standard 2-armed chromosomes. The 2 most frequent scenarios were separation of sister chromatids in anaphase I or monopolar/bipolar attachment of the univalent to the spindle apparatus with unseparated chromatids. Misdivision was rare, and its frequency appeared directly related to the size of the centromere. The previously deduced relationship between misdivision frequency and chromosome size was likely erroneous and can be explained by a general relationship between chromosome length and the size of its centromere. Pairing of identical arms in isochromosomes did not protect them from misdivision. It is not chiasmate pairing that protects from misdivision but mechanistic issues that arise through that pairing.
          Cover page: Misdivision of Telocentrics and Isochromosomes in Wheat
          • Article
          • Peer Reviewed
          UC Riverside Previously Published Works (2017)
            Cover page: Re‐Engineering of the Pm21 Transfer from Haynaldia villosa to Bread Wheat by Induced Homoeologous Recombination
            • Article
            • Peer Reviewed
            UC Riverside Previously Published Works (2014)

            Premise of the study

            Wide hybridization followed by spontaneous chromosome doubling of the resulting hybrids plays an important role in plant speciation. Such chromosome doubling is usually accomplished via unreduced gametes produced by altered meiosis, the so-called 'meiotic restitution'. Unreduced gametes are expected to carry somatic chromosome numbers and constitutions. However, it has been shown recently that new allopolyploids often carry unusual chromosome constitutions which include compensating and noncompensating nulli-tetrasomies and monotrisomies, and translocations of homoeologues.

            Methods

            We have reanalyzed meiotic divisions in a wheat-rye hybrid by in situ probing with labeled DNA focusing on deviations from the standard pattern of meiotic restitution.

            Key results

            In a typical first division restitution in a wide hybrid, there is no chromosome pairing, univalents separate sister chromatids in anaphase I, and there is no meiosis II. Here we illustrate that occasional pairing of homoeologous chromosomes in metaphase I, combined with separation of sister chromatids of univalents, generates diads with compensating nulli-disomies and associated translocations of homoeologues. Similarly, precocious metaphase I migration to the poles of some undivided univalents generates a wide range of noncompensating simple and complex nulli-disomies in the gametes.

            Conclusions

            Both alterations to the standard pattern of meiotic restitution tend to maintain the somatic chromosome numbers in the gametes; chromosome constitutions are variable but mostly genetically balanced. This source of variation among progeny may be an important factor contributing to greater success of natural allopolyploids.
              Cover page: The origin of unusual chromosome constitutions among newly formed allopolyploids
              • Article
              • Peer Reviewed
              UC Riverside Previously Published Works (2016)

              Key message

              By removing the Rf (multi) locus from chromosome 1BS of wheat via chromosome engineering we were able to generate a resource for the production of male sterile wheats in three new cytoplasms. Cytoplasmic male sterility is an essential component in the development of many hybrid crops. In wheat (Triticum aestivum L.) only the cytoplasm of T. timopheevi cytoplasm has been extensively tested even though many other cytoplasms are also known to produce male sterility. Among them are the cytoplasms of Ae. kotschyi, Ae. uniaristata and Ae. mutica but here male sterility manifests itself only when the 1RS.1BL rye-wheat translocation is present in the nuclear genome. The location of the male fertility restoring gene on the chromosome arm 1BS (Rf (multi) ) has recently been determined using a set of primary recombinants of chromosome arms 1RS with 1BS. Using this knowledge the same recombinants were used to create chromosome arm 1BS in wheat with a small insert from rye that removes the restorer locus. The disomic engineered chromosome 1B1:6 assures male sterility in all three cytoplasms and any standard chromosome 1B in wheat is capable of restoring it. This newly engineered chromosome in combination with the three cytoplasms of Aegilops sp extends the range of possibilities in attempts to create a viable system for hybrid wheat production.
                Cover page: Engineering the 1BS chromosome arm in wheat to remove the Rfmulti locus restoring male fertility in cytoplasms of Aegilops kotschyi, Ae. uniaristata and Ae. mutica
                • Thesis
                • Peer Reviewed
                UC Riverside Electronic Theses and Dissertations (2016)

                ABSTRACT OF THE DISSERTATION

                Discovery and Verification of Quantitative Trait Loci (QTL) for Seminal Root Traits and Insights into Root to Shoot Tradeoffs in Hexaploid Wheat (Triticum aestivum L.)

                by

                Christopher E. Hohn

                Doctor of Philosophy, Graduate Program in Plant Biology

                University of California, Riverside, June 2016

                Dr. Adam J. Lukaszewski, Chairperson

                Wheat is among the top three cereal crops with over ca. 600 million tons being harvested annually. In terms of its range of cultivation no other crop can rival wheat. It was first cultivated over 10,000 years ago as humans shifted from hunting and gathering to settled agriculture. Since then wheat has seen more than a threefold increase in grain yield and makes up ca. 20% of the human diet. Today climate change and increased incidence of drought in areas a wheat production negatively impact grain yield. This has prompted interest in studying root system traits and how those traits may improve drought tolerance. For these reasons, the research in this dissertation was aimed at identifying quantitative trait loci (QTLs) and allelic variation for root system traits while also gaining an understanding of root and shoot relationships. To accomplish this three integrated mapping populations of bread wheat were created and sets of unique experiments were conducted. Significant variation for root system traits was observed in all three populations and QTLs were identified and verified for some of these traits. One major QTL for seminal root angle on chromosome arm 2DS was verified in two of the three mapping populations. Additionally, we were able to draw some general conclusions about the relationship between root and shoot biomass within the materials we tested. Using over ca. 6,000 data points we observed that as root biomass continues to increase beyond a certain threshold it negatively impacts grain yields and shoot biomass. However, in individual cultivars this relationship may be entirely different, with root biomass increasing proportionately to increasing grain yields without any observable threshold. When testing for allelic variation at a locus thought to control root biomass on rye chromosome arm 1RS we were unable to identify any significant differences between sources of the 1RS translocation. In a similar study testing for allelic variation for a locus on wheat chromosome arm 1BS thought to control root system plasticity in response to drought we were also unable to identify any significant difference between 1B substitution lines in a common genetic background of cv. Pavon 76.

                  Cover page: Discovery and Verification of Quantitative Trait Loci (QTLs) for Seminal Root Traits and Insights Into Root to Shoot Tradeoffs in Hexaploid Wheat (Triticum aestivum L.)
                  • Article
                  • Peer Reviewed
                  UC Riverside Previously Published Works (2024)
                  The cytoplasm of Aegilops kotschyi is known for the induction of male sterility and haploidy in wheat. Both systems originally appeared rather simple, but manipulation of the standard chromosome constitution of the nuclear genome revealed additional interactions. This study shows that while there is little or no allelic variation at the main fertility restorer locus Rfmulti on chromosome arm 1BS, additional genes may also be involved in the nuclear-mitochondrial genome interactions, affecting not only male fertility but also the growth rate, from pollen competition for fertilization and early endosperm divisions all the way to seed size and plant maturity. Some of these effects appear to be of a sporophytic nature; others are gametophytic. Induction of parthenogenesis by a rye inducer in conjunction with the Ae. kotschyi cytoplasm is well known. However, here we show that the cytoplasmic-nuclear interactions affect all aspects of double fertilization: producing maternal haploids from unfertilized eggs, diploids from fertilized eggs or synergids, embryo-less kernels, and fertilized eggs without fertilization of the double nucleus in the embryo sack. It is unclear how frequent the inducers of parthenogenesis are, as variation, if any, is obscured by suppressors present in the wheat genome. Genetic dissection of a single wheat accession revealed five distinct loci affecting the rate of maternal haploid production: four acting as suppressors and one as an enhancer. Only when the suppressing haplotypes are confirmed may it be possible to the identify genetic variation of haploidy inducers, map their position(s), and determine their nature and the mode of action.
                    Cover page: New Observations of the Effects of the Cytoplasm of Aegilops kotschyi Boiss. in Bread Wheat Triticum aestivum L.
                    • Article
                    • Peer Reviewed
                    UC Riverside Previously Published Works (2011)
                    Doubled haploids are an established tool in plant breeding and research. Of several methods for their production, androgenesis is technically simple and can efficiently produce substantial numbers of lines. It is well suited to such crops as hexaploid triticale. Owing to meiotic irregularities of triticale hybrids, aneuploidy may affect the efficiency of androgenesis more severely than in meiotically stable crops. This study addresses the issue of aneuploidy among androgenic regenerants of triticale. Plant morphology, seed set and seed quality were better predictors of aneuploidy, as determined cytologically, than flow cytometry. Most aneuploids were hypoploids and these included nullisomics, telosomics, and translocation lines; among 42 chromosome plants were nulli-tetrasomics. Rye chromosomes involved in aneuploidy greatly outnumbered wheat chromosomes; in C(0) rye chromosomes 2R and 5R were most frequently involved. While the frequency of nullisomy 2R was fairly constant in most cross combinations, nullisomy 5R was more frequent in the most recalcitrant combination, and its frequency increased with time spent in culture with up to 70% of green plants recovered late being nullisomic 5R. Given that 5R was not involved in meiotic aberrations with an above-average frequency, it is possible that its absence promotes androgenesis or green plant regeneration. Overall, aneuploidy among tested combinations reduced the average efficiency of double haploid production by 35% and by 69% in one recalcitrant combination, seriously reducing the yield of useful lines.
                      Cover page: Aneuploidy among androgenic progeny of hexaploid triticale (XTriticosecale Wittmack)
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