
Title: A reverse genetics approach to investigating the role of sucrose synthase in nodule function and metabolism
Author: Horst, Irmtraud
ISNI:       0000 0001 3581 9188
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2008
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Symbiotic nitrogen fixation has played a role in agriculture for thousands of years. Most legumes, such as pea and soybean, are able to form a symbiosis with the soil bacteria rhizobia. A new organ, the nodule, is formed in which rhizobia fix nitrogen in exchange for carbon supplied by the plant. The carbon source transported to the nodule is sucrose derived from photosynthesis. However, sucrose cannot be used directly by the endosymbionts, but has to be cleaved by either sucrose synthase (susy) or invertase. The aim of this study was to establish the role that these two enzymes play in acquisition of nitrogen by the model legume Lotus japonicus through the symbiosis with rhizobia. The expression patterns of six LjSUS genes and two LjINV genes encoding isoforms of susy and invertase, respectively, were analysed in several plant organs. Mutants were isolated via TILLING (Targeting Induced Local Lesions IN Genomes; Perry et al. 2003) for the genes most highly expressed in the nodule - LjSUSl, LjSUS3 and LjINVl. Lines for susl-l, sus3-1, and the double mutant susl-l/sus3-1 lacked LjSUSl, LjSUS3 or both proteins, respectively, and grew at WTrates when supplied with the necessary macro- and micro-nutrients. In contrast, lines with deleterious mutations in LjINVl were impaired in growth indicating that this gene plays a major role in plant development. The sus mutants accumulated sucrose in their nodules with amounts increasing from susl-l, to . sus3-1 and susl-l/sus3-1. Signs of nitrogen starvation were observed when the plants were grown in the absence of nitrogen, the phenotype being most severe in susl-l/sus3-1 mutants. This clearly indicated that invertase was unable to compensate for the loss of nodule susy activity and that LjSUSl and LjSUS3 are necessary for nodule function and metabolism in L. japonicus.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available