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Master Thesis

Rôle du facteur de transcription ABI5 dans la vigueur et la longévité des graines de Medicago truncatula

Abstract : ABI5 is a TF family of bZIP that activates or inhibits the transcription of its targets through the ABRE motifs in their promoters. The role of this TF is still unknown, but in Arabidopsis, it is involved in transcription of the LEA genes AtEM6 AtEM1 and plays a role in postgerminative growth arrest in response to ABA. Previous results from the research team demonstrated a role for ABI5 in seed dormancy and longevity of Medicago truncatula ssp tricycla. Here, we screened and phenotyped several abi5 mutants: Tnt1 Mtabi5, RNAi Mtabi5 and overexpressors of MtABI5 containing the repressor motif EAR. Seeds of the 35S::MtABI5_EAR did not show any ABA insensitivity, but they lacked dormancy and had a slightly reduced longevity. For seeds of the Tnt1 insertion mutants, longevity was strongly decreased and RFO sugar content was reduced. Seeds were not dormant and desiccation tolerance could be re-induced in germinated radicles, in contrast to wild type seeds. To determine putative targets, MtABI5 was ectopically expressed in hairy roots, followed by a microarray analysis to identify differentially expressed genes. The comparison of these data with the transcriptome of Tnt1 Mtabi5 mutants suggests that MtABI5 induces the expression of two ZEP genes, implicated in ABA synthesis, during maturation and represses two ABA 8' hydroxylases, involved in ABA degradation, around seed abscission. ABA contents are lower in the Mtabi5 and 35S::MtABI5_EAR seeds. We hypothesize MtABI5 is implicated in the acquisition and maintenance of seed dormancy via ABA modulation. MtABI5 also appears to be involved in the repression of genes involved in photosynthesis, concomitant with the loss of chlorophyll in the seeds during maturation.
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Master Thesis
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Julia Zinsmeister. Rôle du facteur de transcription ABI5 dans la vigueur et la longévité des graines de Medicago truncatula. Sciences agricoles. 2013. ⟨dumas-00973439⟩

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