cGMP dependent modulation of cation transport in plants

The cyclic nucleotide cGMP is present in plant cells. In addition, its concentration has been shown to change 5 to 10-fold in response to several stimuli showing it acts as a true second messenger. cGMP has a role in phytochrome signalling, alpha-amylase production, defense responses and many other mechanisms. Furthermore, the participation of cGMP in the modulation of ionic fluxes has been reported in several studies: Exposure of protoplasts to membrane permeable cGMP led to a rapid influx of Ca2+; during stomatal functioning cGMP directly affects K+ fluxes that generate turgor changes; cation conducting cyclic nucleotide gated channels are activated by cyclic nucleotides; non-selective ion channels in Arabidopsis root plasma membranes are inhibited by cGMP. At the tissue level, net Na+ uptake and Na+ accumulation, Na+ efflux and K+ uptake are all affected by cGMP. In addition, we recently showed that cGMP modulates transcription of many genes particularly those involved in cation transport. This proposal is therefore aimed at building on these observations and to study (i) which specific transporters are involved in cGMP modulated Na+ and K+ fluxes and (ii) what the basic principles are of plant cGMP based signalling. Ultimately such knowledge may help in understanding important aspects of plant mineral nutrition such as K+ uptake and homeostasis, and plant tolerance to salinity stress

cGMP has a role in phytochrome signalling, alpha-amylase production, defense response and many other processes. Furthermore, the participation of cGMP in the modulation of ionic fluxes has been reported in several studies: In protoplasts, exposure to membrane permeable cGMP leads to a rapid influx of Ca2+ , during stomatal functioning cGMP affects K+ fluxes, cation conducting cyclic nucleotide gated channels are activated by cyclic nucleotides, and non-selective ion channels in Arabidopsis root plasma membranes are inhibited. At the tissue level, net Na+ uptake and Na+ accumulation, Na+ efflux and K+ uptake are all affected by cGMP. In addition, we recently showed that cGMP modulates transcription of many genes particularly those involved in cation transport. This proposal is aimed at building on these observations and to study (i): Which specific transporters are involved in cGMP modulated Na+ and K+ fluxes. Knockout (KO) lines have been acquired for cation transporters which were shown to be significantly regulated by cGMP and for cation transporters that have cyclic nucleotide binding sites. These lines will be compared to wildtype plants regarding Na+ flux and accumulation and K+ influx to identify cGMP transporter targets. (ii) How does cGMP signal transduction occur in plants. We will test whether the latter involves generic protein phosphorylation, as is the case in mammalian cells, by using a phosphoproteomics approach. We will examine the role of putative cyclic nucleotide dependent and other type kinases in cGMP dependent phosphorylation and the role of phosphorylation as intermediate in cGMP dependent transcriptional regulation. By using cameleon as a Ca2+ reporter the interaction between Ca2+ and cGMP signalling will be assessed and the role of Ca2+ as intermediate in cGMP dependent transcriptional regulation