Genome-wide survey of the seagrass Zostera muelleri suggests modification of the ethylene signalling network.

Agnieszka A Golicz,Martin Schliep,Huey Tyng Lee,Anthony W.D Larkum,Jacqueline Batley,Rudy Dolferus,David Edwards,Chon-Kit Kenneth Chan,Gaurav Sablok,Peter J Ralph

doi:10.1093/jxb/eru510

Abstract

Seagrasses are flowering plants which grow fully submerged in the marine environment. They have evolved a range of adaptations to environmental challenges including light attenuation through water, the physical stress of wave action and tidal currents, high concentrations of salt, oxygen deficiency in marine sediment, and water-borne pollination. Although, seagrasses are a key stone species of the costal ecosystems, many questions regarding seagrass biology and evolution remain unanswered. Genome sequence data for the widespread Australian seagrass species Zostera muelleri were generated and the unassembled data were compared with the annotated genes of five sequenced plant species (Arabidopsis thaliana, Oryza sativa, Phoenix dactylifera, Musa acuminata, and Spirodela polyrhiza). Genes which are conserved between Z. muelleri and the five plant species were identified, together with genes that have been lost in Z. muelleri. The effect of gene loss on biological processes was assessed on the gene ontology classification level. Gene loss in Z. muelleri appears to influence some core biological processes such as ethylene biosynthesis. This study provides a foundation for further studies of seagrass evolution as well as the hormonal regulation of plant growth and development.

Highlights

Seagrasses are a polyphyletic group of monocotyledonous plants which are capable of living underwater in marine environments (Larkum et al, 2006; Waycott et al, 2006)
With the estimated coverages being 30× and above, all of the two genomes should be sampled according to Lander–Waterman statistics (Lander and Waterman, 1988), so the gene loss presented here is unlikely to be due to uneven sampling of the genome
Whole-genome shotgun sequence data for the seagrass species Z. muelleri was compared with gene sets of four sequenced terrestrial species, A. thaliana, O. sativa, P. dactylifera, and M. acuminata, and one aquatic species S. polyrhiza

Summary

Introduction

Seagrasses are a polyphyletic group of monocotyledonous plants which are capable of living underwater in marine environments (Larkum et al, 2006; Waycott et al, 2006) They are descendants of terrestrial plants which returned to life in the aquatic environment and consist of ~60 species, most of which have long narrow leaves and grow in large submerged meadows (Wissler et al, 2011). Seagrasses have evolved to grow and reproduce under these difficult environmental conditions, emphasizing a unique/novel morphology, physiology, and biochemistry compared with terrestrial plants They have developed aerenchyma in their leaves, roots, and rhizomes to tolerate anoxia; stomata are absent; and they have reduced stamen and corolla and elongated pollen without an exine layer to facilitate hydrophilous pollination. The characterization of genes that are lost in seagrass compared with other plant species suggests which molecular processes are no longer active or have significantly diverged in seagrass, while the identification of conserved genes between seagrasses and other plants can help resolve processes that are indispensable to plant life both on land and in the marine realm

Methods

Results

Conclusion