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: Wednesday 30 November 2011 Rhizobium-legume symbiosis is an ecologically friendly source of nitrogen to improve soil fertility. Nitrogen-fixing Rhizobia are situated in root nodule in a specialized endosomes called symbiosomes (SBs). Host plant derived SB membrane (SM) is the interface providing the metabolic exchange between two partners. During the development SBs are multiplying and growing in volume more than 40 times. We have performed the quantitative estimation of nodule infected cell structures in the course of symbiosis using 3D reconstruction of confocal images of Medicago truncatula. We have specified the particular cell layer with the highest level of symbiosomes growth. Surprisingly in this cell layer host cell vacuole volume was drastically diminished. We hypothesized that transport of water is redirected in this cell layer from vacuole to bacteroids and potential symbiosome membrane aquaporins should be involved. Q-PCR analysis of 6 tonoplast aquaporins expression level has revealed that MtTIP1g is significantly upregulated. The localization of GFP-tagged MtTIP1g has shown host tonoplast labeling in all nodule cells, but SMs acquired GFP only in the cell layer where most rapid growth of SBs happens. Functional analysis of MtTIP1g in root nodules using an RNAi method showed that partial silencing of MtTIP1g is causing the arrest of SBs development and preventing the formation of nitrogen-fixing SBs. According to our previous data symbiosome membrane has mixed identity and coopting the molecular markers of exo- and endocytotic pathway (Limpens et al., 2009). It is established that SBs are accepting plasma membrane identity immediately after being released to host cell, but the identity of young vacuole it obtains much later. The functional significance of this identity change was not known. Our data are providing the clue to functionality of SM identity. The acceptance of vacuole identity is crucial as it permits to recruit vacuolar proteins like MtTIP1g and promote an extremely rapid and robust SBs growth. Limpens et al., Plant Cell 21: 2811–2828 (2009). Concurrent Session 11 – Nodule Formation 1100 – 1230 Authors: Aleksandr Gavrin 1 , Sergey Ivanov 1 , Ton Bisseling 1 , Elena Fedorova 1 1 Laboratory of Molecular Biology, Wageningen University, Wageningen, 6708PB, The Netherlands Presentation Title: The role of symbiosome membrane aquaporin MtTIP1g in bacteroids growth and maturation Presentation Time: 1200 - 1220 74 2011
17 th International Congress on Nitrogen Fixation Fremantle, Western Australia 27 November – 1 December 2011 Session Details: Wednesday 30 November 2011 Concurrent Session 12 – PGPR & Plant Production 1100 – 1230 Authors: Sharon Fox 1 , Graham O‟Hara 1 and Lambert Bräu 1 1 Centre for Rhizobium Studies, Murdoch University, Murdoch, 6150, Western Australia. Presentation Title: Differential effects of Pseudomonas fluorescens WSM3457 on enhanced Medicago nodulation Presentation Time: 1100 - 1120 Pseudomonas fluorescens WSM3457 has been studied as a nodulation increasing bacteria (NIB) since 2006 due to increases in the nodulation of subterranean clover reported in glasshouse and field trials. We have demonstrated a similar phenomenon on the Medicago truncatula / Sinorhizobium medicae WSM419 symbiosis. During glasshouse trials it was observed that co-inoculation results in larger, pinker nodules, located higher on the root system, compared to M. truncatula inoculated with only S. medicae WSM419. Nodule location suggested that nodules were elicited earlier on co-inoculated plants and this was confirmed during studies comparing the rate of nodule initiation on M. truncatula inoculated with either S. medicae WSM419 or both WSM419 and P. fluorescens WSM3457. The results also demonstrated that there was a significant increase in symbiotic effectiveness, both in terms of plant mass and total fixed N. Following those results it was investigated whether co-inoculation increased the effectiveness of a partially effective symbioisis, namely that of the symbiosis between S. meliloti 1021 with M. truncatula. The results show that there was no significant increase in shoot mass with co-inoculation with P. fluorescens WSM3457. However, the nodulation data tells a conflicting story, with enhanced nodulation scores on M. truncatula when P. fluorescens WSM3457 was co-inoculated with S. meliloti 1021. 75 2011
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INVENTING THE FUTURE IN INOCULANTS
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