The C<sub>4</sub> photosynthetic pathway acts to concentrate CO<sub>2</sub> around the enzyme Ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco), ensuring that it catalyses a carboxylation rather than oxygenation reaction, which in turn suppresses photorespiration. In nearly all cases C<sub>4</sub> photosynthesis is underpinned by characteristic Kranz anatomy, with concentric wreaths of bundle sheath (BS) and mesophyll (M) cells surrounding closely spaced veins. The increased yields associated with the C<sub>4</sub> pathway have lead to the suggestion that C<sub>3</sub> crops such as rice should be engineered to undertake C<sub>4</sub> photosynthesis, however, this goal is currently held back by a lack of understanding about how the development of Kranz anatomy is regulated. Recently, a number of candidate Kranz regulators have been identified in an RNA-seq study that compared leaf development in maize foliar (Kranz) and husk (non-Kranz) leaves. However, this study did not consider the impact of a recent whole genome duplication in the maize lineage on the gene expression patterns analysed. Therefore, in this thesis maize homeolog gene-pair divergence during early leaf development was assessed. This revealed that expression divergence of homeolog gene-pairs is a significant evolutionary phenomenon. Functional validation of a subset of Kranz candidates revealed that a Zmscr1-1; Zmscr1h-1 double mutant exhibited defects in Kranz patterning, including increased formation of extra BS cells and veins with no separating M cells. Furthermore, Zmnkd1; Zmnkd2 double mutants exhibited a subtle increase in extra BS cell formation. Taken together, this indicates that both ZmSCR1/ZmSCR1h and ZmNKD1/ZmNKD2 function redundantly during Kranz development. No evidence was obtained that two additional genes, ZmSHR2 and ZmRVN1, play a role in Kranz development, and expression of candidate Kranz regulators in rice did not alter leaf anatomy. Together, this work has confirmed roles for a number of genes in Kranz regulation, and has provided insight into the complex regulation underpinning Kranz development in maize.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:730087 |
| Date | January 2016 |
| Creators | Hughes, Thomas |
| Contributors | Langdale, Jane |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://ora.ox.ac.uk/objects/uuid:86184e64-c7bb-43e9-9320-0ebbb2793ea8 |
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