Cyclic Nucleotide Gated Channels

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Cyclic Nucleotide Gated Channels (CNGCs) in Selaginella

The genomes of Selaginella were screened for the occurrence of characteristic fingerprints known from plant cation channels that are putatively regulated by cyclic nucleotides (CNGCs). In total in each of the two sequenced genomes 6 loci coding for CNGC subunits could be identified and were named SmCNGC1, SmCNGC2, SmCNGC3, SmCNGC4, SmCNGC5, and SmCNGC6. Functional channels are proposed to be formed by the assembly of four of such subunits. So far it is not known whether the assembly only occurs between identical subunits (homomers) or whether also heteromeric channels are formed.

The six polypeptides (SmCNGC1, SmCNGC2, SmCNGC3, SmCNGC4, SmCNGC5, SmCNGC6) were grouped together with CNGCs from Arabidopsis thaliana and Physcomitrella patens.


Phylogenetic Analysis

Image:CNGC_Phylo.jpg

Phlylogenetic analysis of CNGCs in Physcomitrella, Selaginella and Arabidopsis. Minimum Evolution (ME) consensus tree under the JTT + Gamma evolutionary model (chosen by ProtTest (Abascal et al., 2005)). Gamma distribution was split into 8 categories to model rate heterogeneity among sites. Bootstrap analysis were done with 500 replicates. Gamma distribution and protein distances were computed with TREE-PUZZLE and PUZZLEBOOT (Schmidt et al., 2002). ME trees were computed with "fitch" from the Software package PHYLIP (Felsenstein, 2005).

The phylogenetic analysis revealed that the four group distribution -initially poposed by Mäser et al. (2001) for CNGCs from Arabidopsis- needs to be revised. Clear orthologs from Physcomitrella and Selaginella could be identified in the groups IV (formerly named Group IVa by Mäser et al., 2001) and V (formerly named Group IVb). The CNGCs from Physcomitrella and Selaginella also support a clear separation between the former Groups IVa and IVb into the new Groups IV and V. In contrast, the CNGCs from Physcomitrella and Selaginella do not support anymore a clear separation into the groups I, II, and III. Instead, on the basis of the current data the three groups have to be gathered into a Supergroup A. It is likely that in future analyses this Supergroup will be sub-partitioned into new Groups that are different from Groups I, II, and III.


Table 1: CNGCs in Arabidopsis thaliana, Physcomitrella patens and Selaginella moellendorffii

Arabidopsis thaliana Physcomitrella patens Selaginella moellendorffii
Name (Protein ID) Name (locus) Name (Protein ID)
AtCNGC 1 (At5g53130)

AtCNGC 2 (At5g15410)

AtCNGC 3 (At2g46430)

AtCNGC 4 (At5g54250)

AtCNGC 5 (At5g57940)

AtCNGC 6 (At2g23980)

AtCNGC 7 (At1g15990)

AtCNGC 8 (At1g19780)

AtCNGC 9 (At4g30560)

AtCNGC 10 (At1g01340)

AtCNGC 11 (At2g46440)

AtCNGC 12 (At2g46450)

AtCNGC 13 (At4g01010)

AtCNGC 14 (At2g24610)

AtCNGC 15 (At2g28260)

AtCNGC 16 (At3g48010)

AtCNGC 17 (At4g30360)

AtCNGC 18 (At5g14870)

AtCNGC 19 (At3g17690)

AtCNGC 20 (At3g17700)

PhysA (12171)

PhysB (89882)

PhysC (1388)

PhysD (77922)

PhysE (192635)

PhysF (230287)

PhysG (121780)

PhysH (41001)

SmCNGC1 (234015)

SmCNGC2 (112824)

SmCNGC3 (266514)

SmCNGC4 (129465)

SmCNGC5 (145167)

SmCNGC6 (89324)

Possible physiological functions of CNGCs in Selaginella

The role of CNGCs in plants is currently under investigation. With respect to Selaginella it is remarkable that SmCNGC2 and SmCNGC4 group together with AtCNGC2 and AtCNGC4 in the well defined Group IV. AtCNGC2 and AtCNGC4 are the best investigated CNGCs. Forward and reverse genetic approaches clearly showed their role in pathogen response(Clough et al., 2000; Balagué et al., 2003) and plant development(Köhler et al., 2001; Chan et al., 2003). Both, Atcngc2 and Atcngc4 mutants show strong phenotypes: a 'Defense No Death' phenotype, i.e. increased salicylic acid levels, constitutive expression of defense-related genes, no hypersensitive response (Clough et al., 2000) and dwarfism and low fertility (Balagué et al., 2003). In case of Atcngc2 both phenotypes were linked to impaired signaling pathways (Chan et al., 2003; Ali et al. 2007). Interestingly, a few alleles of a lesion-mimic mutant of barley are also caused by the lack of function of a CNGC, which in sequence is most similar to that of AtCNGC4 (Rostoks et al., 2006). Therefore, CNGCs are involved in plant defense against pathogens in both dicotyledon and monocotyledon plants.

It might therefore be a working hypothesis that in Selaginella SmCNGC2 and SmCNGC4 play a role in defense mechanisms.

References

  • Abascal F, Zardoya R, Posada D (2005) ProtTest: Selection of best-fit models of protein evolution. Bioinformatics 21:2104-2105.
  • Ali R, Ma W, Lemtiri-Chlieh F, Tsaltas D, Leng Q, von Bodman S, Berkowitz GA (2007) Death don't have no mercy and neither does calcium: Arabidopsis CYCLIC NUCLEOTIDE GATED CHANNEL2 and innate immunity. Plant Cell 19:1081-1095.
  • Balagué C, Lin B, Alcon C, Flottes G, Malmström S, Köhler C, Neuhaus G, Pelletier G, Gaymard F, Roby D (2003) HLM1, an essential signaling component in the hypersensitive response, is a member of the cyclic nucleotide-gated channel ion channel family. Plant Cell 15:365-379.
  • Chan CW, Schorrak LM, Smith RK Jr, Bent AF, Sussman MR (2003) A cyclic nucleotide-gated ion channel, CNGC2, is crucial for plant development and adaptation to calcium stress. Plant Physiol. 132:728-731.
  • Clough SJ, Fengler KA, Yu IC, Lippok B, Smith RK Jr, Bent AF (2000) The Arabidopsis dnd1 "defense, no death" gene encodes a mutated cyclic nucleotide-gated ion channel. PNAS 97:9323-9328.
  • Felsenstein J (2005) PHYLIP (Phylogeny Inference Package) version 3.6. Distributed by the author. Department of Genome Sciences, University of Washington, Seattle.
  • Köhler C, Merkle T, RobyD, Neuhaus G (2001) Developmentally regulated expression of a cyclic nucleotide-gated ion channel from Arabidopsis indicates its involvement in programmed cell death. Planta 213: 327-332.
  • Mäser P, Thomine S, Schroeder JI, Ward JM, Hirschi K, Sze H, Talke IN, Amtmann A, Maathuis FJ, Sanders D, Harper JF, Tchieu J, Gribskov M, Persans MW, Salt DE, Kim SA, Guerinot ML (2001) Phylogenetic relationships within cation transporter families of Arabidopsis. Plant Physiol. 126:1646-1667.
  • Rostoks N, Schmierer D, Mudie S, Drader T, Brueggeman R, Caldwell DG, Waugh R, Kleinhofs A (2006) Barley necrotic locus nec1 encodes the cyclic nucleotide-gated ion channel 4 homologous to the Arabidopsis HLM1. Mol Genet Genomics 275:159-168.
  • Schmidt HA, Strimmer K, Vingron M, von Haeseler A (2002) TREE-PUZZLE: maximum likelihood phylogenetic analysis using quartets and parallel computing. Bioinformatics 18:502-504.


More Information

For further information and questions please contact:

Ingo Dreyer <dreyer at uni-potsdam.de>

Luiz Gustavo Guedes Correa <correa at uni-potsdam.de>

Barbara Köhler <bakoehl at uni-potsdam.de>

Diego Mauricio Riaño-Pachón <diriano at uni-potsdam.de>

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