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First published online September 17, 2009; doi:10.3732/ajb.0900067 American Journal of Botany 96: 1830-1838 (2009) © 2009 Botanical Society of America, Inc.

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Differential expression of candidate salt-tolerance genes in the halophyte Helianthus paradoxus and its glycophyte progenitors H. annuus and H. petiolaris (Asteraceae)¹

² University Paris-Sud, UMR 0320 / UMR 8120 Génétique Végétale, F-91190 Gif-sur-Yvette, France ³ University of British Columbia, Department of Botany, Vancouver, BC V6T 1Z4, Canada ⁴ ETH Zurich, Institute of Integrative Biology, Universitätstrasse 16, 8092 Zurich, Switzerland

ABSTRACT

Adaptation to different habitats is considered to be a major force in the generation of organismal diversity. Understanding the genetic mechanisms that produce such adaptations will provide insights into long-standing questions in evolutionary biology and, at the same time, improve predictions of plant responses to changing environmental conditions. Here we used semiquantitative RT-PCR to study the expression of eight candidate salt-tolerance genes in leaves of the highly salt-tolerant diploid hybrid species Helianthus paradoxus and its salt-sensitive progenitor species H. annuus and H. petiolaris. Samples were collected after germination and growth under four different treatments: nonsaline (control), near-natural saline, saline with increased K⁺, and saline with decreased Mg²⁺ and Ca²⁺. Three individuals from three populations per species were used. The hybrid species H. paradoxus constitutively under- or overexpressed genes related to potassium and calcium transport (homologues of KT1, KT2, ECA1), suggesting that these genes may contribute to the adaptation of H. paradoxus to salinity. In two other genes, variation between populations within species exceeded species level variation. Furthermore, homologues of the potassium transporter HAK8 and of a transcriptional regulator were generally overexpressed in saline treatments, suggesting that these genes are involved in sustained growth under saline conditions in Helianthus.

Key Words: Asteraceae • habitat adaptation • gene expression • Helianthus annuus • Helianthus paradoxus • Helianthus petiolaris • salinity • salt-tolerance genes • semiquantitative RT-PCR

Received for publication 26 February 2009. Accepted for publication 23 June 2009.

FOOTNOTES

¹ The authors thank M. King for extracting sequences from the Compositae Genome Project database. SK was supported by grant 1777/1-1 of the Deutsche Forschungsgemeinschaft (DFG).

⁵ Author for correspondence (e-mail: sophie.karrenberg{at}env.ethz.ch)

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