IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

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17 th International Congress on Nitrogen Fixation Fremantle, Western Australia 27 November – 1 December 2011 Session Details: Tuesday 29 November 2011 Concurrent Session 8 – Plant Symbiotic Genes 1600 – 1720 Authors: Nijat Imin 1 , Isabel Saur 1 , Nadiatul Radzman 1 , Marie Oakes 1 , Michael A Djordjevic 1 1 Plant Science Division and A. R. C. Centre of Excellence for Integrative Legume Research , Research School of Biology, Canberra, 0200, Australia. Presentation Title: Nodule specific CLE peptides mediate crosstalk between local nodule development and systemic autoregulation of nodulation pathways Presentation Time: 1640 – 1700 Root nodulation is controlled by the local Nod Factor and cytokinin-dependent pathways and systemically by the autoregulation of nodulation (AON) pathway (1). The AON pathway controls nodule number by suppressing nodulation competency in yet-to-be-infected roots via the shoot-expressing SUNN receptor kinase (1-3). Recently, MtCLE12 and MtCLE13, which show nodule-specific expression and encode CLE (CLAVATA3/ESR) peptide ligands, have been shown to regulate AON (3). The ectopic expression of MtCLE12 or MtCLE13 (but not MtCLE26 which does not have nodule specific expression) abolishes nodulation in wild type roots but not in the super nodulating null mutant sunn-4. This suggests that root MtCLE12 or 13 over-expression triggers constitutive AON which suppresses nodulation competency in a SUNN-dependent manner. Using qRT-PCR, we show that three local nodulation pathway genes: NODULE INCEPTION (NIN, a common regulator of the Nod Factor and cytokinin pathways), MtEFD (ethylene response factor and negative regulator of nodule differentiation) and MtRR8 (a type-A response regulator involved in negatively regulating cytokinin signaling) are each regulated specifically by MtCLE12 in a SUNN-dependent manner. This suggests that MtCLE12 expression in the first formed nodules influences shoot SUNN to produce the AON signal that travels to the yet-to-be infected roots to up regulate MtEFD and MtRR8 to reduce nodulation competency by down regulating NIN. This would suppress local Nod Factor and cytokinin signaling at a common point: NIN. This proposed model links for the first time the pathways for Nod factor signaling, cytokinin perception and AON and provides a means for the plant to exert a mechanism to regulate nodule numbers in tune with its physiological status. 58 2011
17 th International Congress on Nitrogen Fixation Fremantle, Western Australia 27 November – 1 December 2011 Session Details: Tuesday 29 November 2011 Concurrent Session 8 – Plant Symbiotic Genes 1600 – 1720 Authors: Senjuti Sinharoy 1 , Ivone Torres-Jerez 1 , Catalina Pislariu 1 , Mingyi Wang 1 , Vagner Benedito 2 and Michael Udvardi 1 1. Samuel Roberts Noble Foundation, Plant Biology Division, Ardmore, Oklahoma 73401 2. West Virginia University, Division of Plant & Soil Sciences, Morgantown, West Virginia 26506 Presentation Title: Identification & functional characterization of Medicago truncatula transcription factor Presentation Time: 1700 – 1720 mutants with impaired symbiotic nitrogen fixation Transcriptomic studies have revealed that thousands of plant genes are involved in symbiotic nitrogen fixation (SNF). Approximately two hundred transcription factor (TF) genes are under spatial control during nodule development (Pislariu et al.,unpublished data), indicating that they may have an important roles in establishing successful symbiosis. Very few TFs have been described that are required for SNF. To understand nodule organogenesis more deeply we need to characterize many more nodule TFs and the gene networks that they control. We constructed hypothetical gene regulatory networks consisting of TFs and their putative targets, based on correlation analysis of spatio-temporal gene expression data. Subsets of nodule-expressed TFs were chosen for further characterization. Medicago mutants with Tnt1-insertions in the chosen TFs were identified by a PCR-based screen of DNA pooled from the mutant population. Thirty one mutant lines with insertions in thirteen different TF genes were identified and phenotyped. Several mutants were found to have altered SNF. Mutants affected in a C2H2-TF gene were characterized in detail. Microscopical analysis of mutant nodules 12 days post inoculation (DPI) indicated that bacteria were released from infection threads and surrounded by the symbiosome membrane, but remained small and did not elongate like bacteroids in wild type nodules. At 15 DPI, mutant nodules were dark/black in color, possibly the result of defense responses triggered after bacterial endocytosis, based on microscopical observations. Expression of the C2H2-TF gene in wild-type nodules was detected first at 4-DPI and increased around 1600 fold by 8-DPI, with highest expression in nodule zone II (invasion-zone) followed by zone III (inter-zone), consistent with the phenotype of the mutant. To identify possible target genes of the C2H2 TF, transcriptome analysis of mutant and wild-type nodules and of p35S::C2H2-TF and p35S::GFP-transformed roots was carried out, using the Affymetrix Medicago GeneChip. Detailed results and analysis of this work will be presented. 59 2011
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