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GlutathloNe and gene regulation

Final Activity Report Summary - GINGER (Glutathlone and gene regulation)

Legumes are one of the most important crops, providing the major source of proteins and oil and improving the nitrogen (N2) soil fertilisation. The plants belonging to this family can make a symbiosis with ground bacteria, Rhizobium spp., to produce a particular root organ, the nodule, able to reduce the atmospheric N2 to ammonia (NH3+), exported and assimilated by the plant. In parallel, the host plant gives the symbiont the carbon source to make the fixing reaction. The useful association between plants and bacteria makes the legumes one of the most interesting 'improving crop' for soil, from an agronomical point of view.

The improvement of the nitrogen fixing performance will allow a better plant production and will facilitate the use of legumes. In this framework, our team is studying the involvement of glutathione (GSH) and its legume specific homologue, homoglutathione (hGSH), two major antioxidant molecules which have important roles in plant defence against biotic and abiotic stresses, storage of reduced sulphur and redox control of the cell, in the nitrogen fixation. Recently, our team has shown that (h)GSH has a key role in the nodulation process.

In this framework, the GINGER project was aimed to examining the molecular targets of the plant (h)GSH pool during the nodulation process performing a transcript profile analysis using a cDNA - Amplification fragment length polymorphism (AFLP) protocol. Using this model, we studied the effect of prior depletion of (h)GSH to investigate whether there are patterns of gene regulation that require (h)GSH. A collection of 181 gene tags classifiable in two clusters and showing (h)GSH-dependent expression changes at different time points during the first 4 days of the nodulation process was obtained.

The cDNA-AFLP transcription analysis showed that transcripts of genes related to the chromatin and DNA metabolism class accumulate at higher levels in control plants compared to (h)GSH depleted plants. The nodulation process involves major cytoskeletal rearrangements and cell wall formation for the infection proliferation within the nodule. At a transcriptomic level, these biological responses are based on the induction of genes associated to the cytoskeleton and to the cell wall formation. Our results show that the expression of genes associated to cytoskeleton was affected by (h)GSH deficiency, suggesting that reorganisation and proliferation of cytoskeletal elements occurring during early nodule development are directly or indirectly regulated by GSH. Similarly, genes belonging to the cell wall metabolic class were less expressed following GSH depletion. Taken together, these results suggest that GSH deficiency affects the infection process during nodulation.

A significant higher expression of genes belonging to defence and cell rescue class was observed in (h)GSH depleted plants. Several genes belonging to other metabolic classes but involved in multiple aspects of the plant defence exhibited a similar behaviour. These results may indicate that (h)GSH deficiency modifies the early plant defense reaction occurring after Rhizobium inoculation.

In conclusion, the characterisation of genes regulated by (h)GSH during the nodulation process increase our knowledge of the cellular regulation by redox state or / and levels of(h)GSH. These data are gainful not only for the legume / Rhizobium scientific research community but also in the plant-microbe interaction and plant development research fields such as cell differentiation, meristem development and redox state control of the cell metabolism.