Genome Size Evolution and Dynamics in Iris, with Special Focus on the Section Oncocyclus.

Elie Saliba,Magda Bou Dagher-Kharrat,Oriane Hidalgo,Sonja Siljak-Yakovlev,Ilia J Leitch,Nour Abdel Samad,Kit Strange

doi:10.3390/plants9121687

Abstract

Insights into genome size dynamics and its evolutionary impact remain limited by the lack of data for many plant groups. One of these is the genus Iris, of which only 53 out of c. 260 species have available genome sizes. In this study, we estimated the C-values for 41 species and subspecies of Iris mainly from the Eastern Mediterranean region. We constructed a phylogenetic framework to shed light on the distribution of genome sizes across subgenera and sections of Iris. Finally, we tested evolutionary models to explore the mode and tempo of genome size evolution during the radiation of section Oncocyclus. Iris as a whole displayed a great variety of C-values; however, they were unequally distributed across the subgenera and sections, suggesting that lineage-specific patterns of genome size diversification have taken place within the genus. The evolutionary model that best fitted our data was the speciational model, as changes in genome size appeared to be mainly associated with speciation events. These results suggest that genome size dynamics may have contributed to the radiation of Oncocyclus irises. In addition, our phylogenetic analysis provided evidence that supports the segregation of the Lebanese population currently attributed to Iris persica as a distinct species.

Highlights

The royal irises (Iris L. subgenus Iris, section Oncocyclus (Siemssen) Baker) have experienced a remarkable radiation across the rocky hillsides, steppes, and deserts of the Middle East, giving rise to c. 33 species [1]
Nucleotide sequence data for 20 Iris species and subspecies have been deposited in the DDBJ/EMBL/GenBank
Our results are consistent with the subgeneric and sectional divisions of the genus Iris, in subgenus Iris most accessions fell in an unresolved polytomy (Figure 1)

Summary

Introduction

The royal irises (Iris L. subgenus Iris, section Oncocyclus (Siemssen) Baker) have experienced a remarkable radiation across the rocky hillsides, steppes, and deserts of the Middle East (incl. the EasternMediterranean and Western Asia regions), giving rise to c. 33 species [1]. These irises exhibit a highly distinctive morphology with a short stem, small falcate leaves arranged in a fan-shaped structure, and, in proportion to the rest of the plant, an oversized solitary flower of varied and complex colour patterns. Flowers of usually dark colour harvest solar energy, a floral heat tightly linked to the night-sheltering bee pollination system which occurs in most species [2,3,4,5]. Shelter mimicry is a rare strategy otherwise restricted to orchids in the Euro-Mediterranean region [4]. A few Oncocyclus species (such as Iris paradoxa Steven) are pollinated through sexual deception—an even more specialised strategy—which is, like shelter mimicry, exclusive to orchids and royal irises in the Euro-Mediterranean. Within the Oncocyclus irises, it has been suggested that sexual deception evolved from shelter mimicry [4]. The pollinator-mediated selection of floral traits is considered a major factor driving diversification in this group, the extent to which it does is still debated [5,6]

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Conclusion