Alasimi, Shiah
(2025)
Identifying novel variation in root anatomical traits for waterlogging and drought tolerance and their genetic basis in wheat and barley.
PhD thesis, University of Nottingham.
Abstract
Climate change threatens crop yields and food security through changes in rainfall patterns associated with increased frequency of waterlogging and drought. In plants, the Ubiquitin mediated proteolysis, through the Plant Cysteine Oxidase (PCO) branch of the PRT6 N-degron pathway, has been identified as a key regulator of plant developmental and environmental responses. Much of the molecular understanding in the PRT6 N-degron pathway has been established in the genetic model Arabidopsis thaliana. However, there is also evidence that at least some of the molecular components of this pathway are conserved in cereals. For example, it has been shown that this pathway controls sensing low oxygen levels during waterlogging as well as affecting responses to drought and salinity in barley. The N-end rule pathway controls plant responses to hypoxia by regulating the stability of the group VII ethylene response factor (ERFVII) transcription factors, controlled by the oxidation status of amino terminal (Nt)-cysteine (Cys).
Root cortical senescence (RCS) is known as a type of programmed cell death found in the Triticeae tribe and studies suggest that RCS reduces water and nutrient uptake, respiration, and radial hydraulic conductance of root tissue. However, it has been argued that RCS can improve growth under suboptimal availability of water and nutrients, and that it can enable the development of crop varieties with improved drought tolerance. However, how the Ndegron pathway may affect root cortical senescence traits in barley and wheat is not fully understood. The objectives of this study were firstly to evaluate the genetic variation of RCS traits and above-ground physiological traits of barley mutants for the PRT6 gene regulating the N-degron pathway under optimum and waterlogged conditions in controlled environment experiments. Secondly, to quantify the genetic variation of RCS traits and aboveground physiological traits and yield and yield components of barley mutants for the Prt6 gene, as well as of wheat Paragon x Watkins landrace lines, under well-watered and drought-stressed conditions in glasshouse experiments. Thirdly, to quantify the soil greenhouse-gas emissions and physiological traits, yield and yield components in the barley PRT6 mutant lines and the wild type in two field experiments under rain-fed conditions. The mutant Prt6 barley lines in these experiments are in the spring barley Sebastian background with three Prt6 allele mutations tested: prt6k, prt6i and prt6 ubrboxc.
Three barley lines containing mutants alleles for the PRT6 gene in barley (prt6i, prt6k and prt6 ubrboxc) and the Sebastian WT parent were phenotyped under controlled and waterlogging conditions in four controlled-environment experiments, and under well-irrigated and drought conditions in two glasshouse experiments. In addition, these lines were phenotype under rainfed conditions in two field experiments. Furthermore, three Paragon × Watkins landrace lines and the wild type Paragon were phenotype under well-watered and drought conditions in the two glasshouse experiments. In each experiment, the quantification of root anatomical traits, including total aerenchyma area and percentage aerenchyma tissue area in root cross-sections, was carried out for the genotypes (calculated as the percentage of air spaces using images of root cross-sections). Above-ground traits, including leaf chlorophyll content (SPAD), tiller number, dry matter accumulation and yield and yield components at harvest were also measured. In addition, greenhouse gas emissions, including CO2 and N20, were measured in the field experiments.
Results in CE and glasshouse experiments showed the percentage root aerenchyma area was increased under abiotic stress (waterlogging or drought), and for barley genotypes the increases were greater in the prt6i alleles than in the Sebastian wild type. In the present experiments, leaf chlorophyll content retention was not enhanced in the PRT6 mutants compared to the Sebastian WT nor was shoot number per plant or plant height enhanced under waterlogging. So, positive effects on improved shoot growth under waterlogging for these PRT6 mutants could not be confirmed in the present experiments. The barley prt6i allele in the present glasshouse experiments did not respond significantly differently to the drought stress for above-ground traits, despite an increase in absolute area of root aerenchyma and percentage aerenchyma area in this line compared to the Sebastian wild type under drought. These results suggest that the percentage aerenchyma area alone is not a sufficient indicator of drought tolerance without taking into consideration other root and above-ground physiological traits. In the field experiments, biomass at maturity was higher in prt6k compared to WT by 4%. Differences in greenhouse gas emissions were found in the field trial in 2023. CO2 and N20 was higher in prt6k allele compared to the WT by 34% and 20%, respectively.
Future studies should explore the complex interactions between aerenchyma formation and other physiological processes to understand their comprehensive impact on waterlogging and drought resilience. One possible explanation for the lack of drought tolerance despite increased aerenchyma area % could be related to its impact on water transport in xylem vessels. Aerenchyma plays a role in facilitating gas exchange in roots, but its increase might interfere with the hydraulic conductivity of xylem vessels. This could happen if the formation of aerenchyma reduces the mechanical strength of roots or alters their ability to transport water efficiently from roots to shoots. Future studies should also address the application of RCS traits and PRT6 mutant alleles for plant breeding for waterlogging and drought tolerance. For example, by introgression of the prt6 alleles into modern elite high-yielding potential backgrounds and by developing molecular markers for screening germplasm for haplotype variation in the PRT6 gene.
| Item Type: |
Thesis (University of Nottingham only)
(PhD)
|
| Supervisors: |
Foulkes, John
Mendiondo, Guillermina |
| Keywords: |
Wheat, barley, root anatomy, waterlogging tolerance, drought tolerance, PRT6 gene, RCS,plant physiology, cereal, stress tolerance |
| Subjects: |
Q Science > QK Botany > QK710 Plant physiology |
| Faculties/Schools: |
UK Campuses > Faculty of Science > School of Biosciences |
| Item ID: |
82259 |
| Depositing User: |
ALASIMI, SHIAH
|
| Date Deposited: |
12 Dec 2025 04:40 |
| Last Modified: |
12 Dec 2025 04:40 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/82259 |
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