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Open Access Research article

Structure and expression of GSL1 and GSL2 genes encoding gibberellin stimulated-like proteins in diploid and highly heterozygous tetraploid potato reveals their highly conserved and essential status

Sathiyamoorthy Meiyalaghan1, Susan J Thomson1, Mark WEJ Fiers14, Philippa J Barrell1, Julie M Latimer1, Sara Mohan12, E Eirian Jones2, Anthony J Conner3 and Jeanne ME Jacobs1*

Author Affiliations

1 The New Zealand Institute for Plant & Food Research Limited, Private Bag 4704, Christchurch 8140, New Zealand

2 Faculty of Agriculture and Life Sciences, Lincoln University, P.O. Box 84, Canterbury 7647, New Zealand

3 AgResearch Ltd, Grasslands Research Centre, Private Bag 11008, Palmerston North 4442, New Zealand

4 Current address: VIB Center for the Biology of Disease, KU Leuven, Herestraat 49, 3000, Leuven, Belgium

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BMC Genomics 2014, 15:2  doi:10.1186/1471-2164-15-2

Published: 2 January 2014

Abstract

Background

GSL1 and GSL2, Gibberellin Stimulated-Like proteins (also known as Snakin-1 and Snakin-2), are cysteine-rich peptides from potato (Solanum tuberosum L.) with antimicrobial properties. Similar peptides in other species have been implicated in diverse biological processes and are hypothesised to play a role in several aspects of plant development, plant responses to biotic or abiotic stress through their participation in hormone crosstalk, and redox homeostasis. To help resolve the biological roles of GSL1 and GSL2 peptides we have undertaken an in depth analysis of the structure and expression of these genes in potato.

Results

We have characterised the full length genes for both GSL1 (chromosome 4) and GSL2 (chromosome 1) from diploid and tetraploid potato using the reference genome sequence of potato, coupled with further next generation sequencing of four highly heterozygous tetraploid cultivars. The frequency of SNPs in GSL1 and GSL2 were very low with only one SNP every 67 and 53 nucleotides in exon regions of GSL1 and GSL2, respectively. Analysis of comprehensive RNA-seq data substantiated the role of specific promoter motifs in transcriptional control of gene expression. Expression analysis based on the frequency of next generation sequence reads established that GSL2 was expressed at a higher level than GSL1 in 30 out of 32 tissue and treatment libraries. Furthermore, both the GSL1 and GSL2 genes exhibited constitutive expression that was not up regulated in response to biotic or abiotic stresses, hormone treatments or wounding. Potato transformation with antisense knock-down expression cassettes failed to recover viable plants.

Conclusions

The potato GSL1 and GSL2 genes are very highly conserved suggesting they contribute to an important biological function. The known antimicrobial activity of the GSL proteins, coupled with the FPKM analysis from RNA-seq data, implies that both genes contribute to the constitutive defence barriers in potatoes. The lethality of antisense knock-down expression of GSL1 and GSL2, coupled with the rare incidence of SNPs in these genes, suggests an essential role for this gene family. These features are consistent with the GSL protein family playing a role in several aspects of plant development in addition to plant defence against biotic stresses.

Keywords:
GSL1; GSL2; Gibberellin stimulated-like proteins; Potato; Snakin; Genome analysis; Transcriptional expression