Involvement of MtABI5 in the acquisition of desiccation tolerance in Medicago truncatula seeds and seedlings: characterization of potential new targets
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(2) Involvement of MtABI5 in the acquisition of desiccation tolerance in Medicago truncatula seeds and seedlings: identification of potential targets Julia Zinsmeister, Emmanuel Terrasson, Julia Buitink, Karima Righetti, Benoît Ly Vu, Sandra Pelletier, David Lalanne, Olivier Leprince Agrocampus-Ouest, UMR 1345 Institut de Recherche en Horticulture et Semences, Angers, France ABI5, a bZIP family transcription factor (TF) is one of the components of the abscisic acid (ABA) signalling pathway in seeds. In Arabidopsis thaliana, it is also involved in tolerance against water stress that induces growth arrest after germination. Our purpose is to investigate the role of MtABI5 in desiccation tolerance (DT) of Medicago truncatula seeds using insertion mutants and transcriptomic analysis.. Mat. 80 60 40 20 0 10. 20. 30. 40. 50. 100. MAT 20 DAP /14 DAP. 2858. RDT 72h PEG /0h PEG. 740. RDT 599 bp. 1034 bp. 60. Gene structure and position of Tnt1 insertions in two mutants of Mtabi5 that were obtained and further characterized for DT.. 40 20 0. 10. 20. 0. 30. 40. 50. 72. Incubation in PEG (hours) PEG. RDT 72h PEG /0h PEG. 8943 2829. Drying +H2O. 3862. 100. 100. 80 60 40 20. WT Mtabi5-1. 0 10. 48 TF →MtABI5. A transcriptomic analysis was performed on the acquisition of DT during seed development (A) and the re-establishment of DT by an osmotic treatment with polyethylene glycol (PEG) (B). (C) A comparative analysis between both datasets revealed 740 genes that are up-regulated (DT-UP) and 2829 genes that are downregulated (DT-DOWN) in relation to DT. MtABI5 is one of the 48 TF present in the UP list.. 80. WT Mtabi5-1 Mtabi5-2. 60 40 20 0. 20 30 40 Days after pollination (DAP). 50. DT DOWN List. DT UP List. 98 125. bZIP. MAT 20 DAP /14 DAP. 2886. 284. 80. Days after pollination (DAP). (C). TGA. % of growing radicles. 100. Mtabi5-2. ATG. Desiccation tolerance (%). (B). Involvement of MtABI5 in DT Mtabi5-1. Desiccation tolerance (%). (A). Desiccation tolerance (%). Identification of transcripts linked to DT. During seed development, no difference in the acquisition of DT was found between wild-type and Mtabi5-1 line. DT was scored as germination after rapid drying at 43% RH and rehydration.. PEG treated. -. +. +. Dried. +. -. +. However, germinated radicles of Mtabi5 mutants were unable to regain DT during PEG treatment, suggesting that MtABI5 is a key component in the reestablishment of DT after germination, but not during development.. MtABI5 affects transcript levels related to biotic defense response during the re-establishment of DT DT UP list. 628. DT DOWN List. Mtabi5 112 RTD. 2152. To identify biological processes that are (in)directly repressed by MtABI5 during re-establishment of DT, a GO analysis was performed. Over-represented GO terms were linked with cell cycle and development. Surprisingly, many genes related to biotic defense were also found, including nucleotide-binding site (NBS)-leucine-rich repeat (LRR) genes, being the largest class of known disease resistance genes effective against pathogens. This suggests that MtABI5 could be involved in a cross-talk between DT and biotic stress tolerance.. Mtabi5 677 RTD. A transcriptome analysis was performed on protruded radicles of Mtabi5 mutants before and after PEG treatment compared to WT radicles (Mtabi5 RTD). Comparison of these data with the DT-UP and DOWN list revealed that 112 of the DT-UP list (15%) were no longer up-regulated in the Mtabi5 mutants whereas 23% (677 transcripts) of the DT-DOWN list were no longer down-regulated in the mutant radicles.. MtABI5 and ABA synthesis during the re-establishment of DT Locus Id Medicago Identification. WT PEG/Cntrl. Mtabi5-1 PEG/Cntrl. Mtabi5-2 PEG/Cntrl. MEDTR5G017330. ZEP. 1.48 (3,535E-05) -1.75 (0.00408919). -1.13 (0.02020474). MEDTR5G017350. ZEP. 2.53 (0.00052403) -1.32 (5.6314E-05). -1.29 (0.00021847). MEDTR5G025610. CYP707A1. -2.43 (1.7196E-05) -0.21(0.32395546). -0.29 (0.45585037). MEDTR8G072260. CYP707A1. -1.16 (0.0090278) -1.65 (0.00727904). -1.07 (0.20385142). Ratios indicate the difference in transcript levels between PEG treated and untreated radicles (Cntrl). P-value is indicated in brackets.. ABA content (pM/mg dry weight). 4,5. 3,5 3 2,5 2 1,5 1 0,5 0. Genes coding for zeaxanthine epoxidases (ZEP, ABA1) that are involved in ABA synthesis were upregulated upon the re-establishment of DT, whereas genes involved in ABA catabolism (CYP707A1, abscisic acid 8'-hydroxylase) were downregulated. Transcript levels of these genes were deregulated in Mtabi5 mutants after PEG treatment. Before PEG treatment After PEG treatment. 4. WT. Mtabi5-1. ABA contents increased in emerged radicles of both WT and Mtabi5-1 mutant emerged radicles after PEG treatment. However, contents were 1.2 fold lower in Mtabi5-1 radicles that remain sensitive to dessication after PEG treatment.. Contact: julia.zinsmeister@agrocampus-ouest.fr.
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