Annexins - calcium- and membrane-binding proteins in the plant kingdom: potential role in nodulation and mycorrhization in Medicago truncatula

Annexins belong to a family of multi-functional membrane- and Ca(2+)-binding proteins. The characteristic feature of these proteins is that they can bind membrane phospholipids in a reversible, Ca(2+)-dependent manner. While animal annexins have been known for a long time and are fairly well characterized, their plant counterparts were discovered only in 1989, in tomato, and have not been thoroughly studied yet. In the present review, we discuss the available information about plant annexins with special emphasis on biochemical and functional properties of some of them. In addition, we propose a link between annexins and symbiosis and Nod factor signal transduction in the legume plant, Medicago truncatula. A specific calcium response, calcium spiking, is an essential component of the Nod factor signal transduction pathway in legume plants. The potential role of annexins in the generation and propagation of this calcium signal is considered in this review. M. truncatula annexin 1 (MtAnn1) is a typical member of the plant annexin family, structurally similar to other members of the family. Expression of the MtAnn1 gene is specifically induced during symbiotic associations with both Sinorhizobium meliloti and the mycorrhizal fungus Glomus intraradices. Furthermore, it has been reported that the MtAnn1 protein is preferentially localized at the nuclear periphery of rhizobial-activated cortical cells, suggesting a possible role of this annexin in the calcium response signal elicited by symbiotic signals from rhizobia and mycorrhizal fungi.

Annexins - calcium- and membrane-binding proteins in the plant kingdom: potential role in nodulation and mycorrhization in Medicago truncatula

Annexins belong to a family of multi-functional membrane- and Ca(2+)-binding proteins. The characteristic feature of these proteins is that they can bind membrane phospholipids in a reversible, Ca(2+)-dependent manner. While animal annexins have been known for a long time and are fairly well characterized, their plant counterparts were discovered only in 1989, in tomato, and have not been thoroughly studied yet. In the present review, we discuss the available information about plant annexins with special emphasis on biochemical and functional properties of some of them. In addition, we propose a link between annexins and symbiosis and Nod factor signal transduction in the legume plant, Medicago truncatula. A specific calcium response, calcium spiking, is an essential component of the Nod factor signal transduction pathway in legume plants. The potential role of annexins in the generation and propagation of this calcium signal is considered in this review. M. truncatula annexin 1 (MtAnn1) is a typical member of the plant annexin family, structurally similar to other members of the family. Expression of the MtAnn1 gene is specifically induced during symbiotic associations with both Sinorhizobium meliloti and the mycorrhizal fungus Glomus intraradices. Furthermore, it has been reported that the MtAnn1 protein is preferentially localized at the nuclear periphery of rhizobial-activated cortical cells, suggesting a possible role of this annexin in the calcium response signal elicited by symbiotic signals from rhizobia and mycorrhizal fungi.

Excessive activation of poly(ADP-ribose) polymerase contributes to inherited photoreceptor degeneration in the retinal degeneration 1 mouse

Retinitis pigmentosa (RP) is an inherited blinding disease for which there is no treatment available. It is characterized by a progressive and neurodegenerative loss of photoreceptors but the underlying mechanisms are poorly understood. Excessive activation of the enzyme poly(ADP-ribose) polymerase (PARP) has recently been shown to be involved in several neuropathologies. To investigate the possible role of PARP in retinal photoreceptor degeneration, we used the retinal degeneration 1 (rd1) mouse RP model to study PARP expression, PARP activity, and to test the effects of PARP inhibition on photoreceptor viability. PARP expression was found to be equal between rd1 and wild-type counterpart retinas. In contrast to this, a dramatic increase in both PARP activity per se and PARP product formation was detected by in situ assays in rd1 photoreceptors actively undergoing cell death. Furthermore, PARP activity colabeled with oxidatively damaged DNA and nuclear translocation of AIF (apoptosis-inducing factor), suggesting activation of PARP as a bridge between these events in the degenerating photoreceptors. The PARP-specific inhibitor PJ34 [N-(6-oxo-5,6-dihydrophenanthridin-2-yl)-N,N-dimethylacetamide x HCl[ reduced the number of cells exhibiting death markers in a short-term retinal culture paradigm, a protective effect that was translated into an increased number of surviving photoreceptors when the inhibitor was used in a long-term culture setting. Our results thus demonstrate an involvement of PARP activity in rd1 photoreceptor cell death, which could have a bearing on the understanding of neurodegenerations as such. The findings also suggest that the therapeutical possibilities of PARP inhibition should include retinal diseases like RP.