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Title: Nitrogen use efficiency in plants : how roots and nodules are balanced in Medicago
Author: Bonyadi Pour, Roxanna
ISNI:       0000 0004 5367 9678
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2014
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Nitrogen availability is central to global food security. Understanding how plants respond to nitrogen could help develop crops with improved nitrogen use. This study aims to investigate how lateral root (LR) and nodule development are balanced in response to low (0.1 mM) and high (5 mM) NH4NO3 concentrations in the model legume Medicago truncatula var. Jemalong A17 using phenotypic and gene regulatory network analysis. High concentrations of NH4NO3 have an inhibitory effect on nodulation. The phenotypic measurements of root architecture of A17 in response to NH4NO3 and rhizobia showed that at high NH4NO3 rhizobia affected LR development. Total root size was less (P < 0.05) in rhizobia inoculated samples compared to the absence of rhizobia. This was due to a shorter primary root and less number of LRs. Whole genome profiling of early (2 and 6 hour) root responses to high NH4NO3 and rhizobia identified 4793 genes that were differentially expressed (significance cutoff of P<0.05). The early (2 and 6 h) responses to high NH4NO3 were mainly independent of the rhizobia effect and N-induction especially at 2 h time point was the predominant response. Some of the components of the autoregulation of nodulation (AON) pathway are also involved in LR development. The sunn-1 mutant is impaired in correct AON signals that lead to hypernodulation with short LRs at low N. Whole genome expression analysis of A17 and sunn-1 root samples identified 7186 significantly (P<0.05) expressed genes showing rhizobia and/or SUNN-regulated responses. These genes could be components of the AON pathway with putative role in balancing the number of nodules with LR development. Using motif analysis tools we identified motifs with putative promoters that were mainly Nodule specific cysteine rich peptides (NCRs). We suggest that these NCRs may be involved in regulating LR and nodule development depending on the plant N status.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: SB Plant culture