Genome-wide identification of ATP binding cassette (ABC) transporter and heavy metal associated (HMA) gene families in f
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RESEARCH ARTICLE
Open Access
Genome-wide identification of ATP binding cassette (ABC) transporter and heavy metal associated (HMA) gene families in flax (Linum usitatissimum L.) Nadeem Khan1,2, Frank M. You1*, Raju Datla3, Sridhar Ravichandran1, Bosen Jia1,2 and Sylvie Cloutier1,2*
Abstract Background: The recent release of the reference genome sequence assembly of flax, a self-pollinated crop with 15 chromosome pairs, into chromosome-scale pseudomolecules enables the characterization of gene families. The ABC transporter and HMA gene families are important in the control of cadmium (Cd) accumulation in crops. To date, the genome-wide analysis of these two gene families has been successfully conducted in some plant species, but no systematic evolutionary analysis is available for the flax genome. Results: Here we describe the ABC transporter and HMA gene families in flax to provide a comprehensive overview of its evolution and some support towards the functional annotation of its members. The 198 ABC transporter and 12 HMA genes identified in the flax genome were classified into eight ABC transporter and four HMA subfamilies based on their phylogenetic analysis and domains’ composition. Nine of these genes, i.e., LuABCC9, LuABCC10, LuABCG58, LuABCG59, LuABCG71, LuABCG72, LuABCG73, LuHMA3, and LuHMA4, were orthologous with the Cd associated genes in Arabidopsis, rice and maize. Ten motifs were identified from all ABC transporter and HMA genes. Also, several motifs were conserved among genes of similar length, but each subfamily each had their own motif structures. Both the ABC transporter and HMA gene families were highly conserved among subfamilies of flax and with those of Arabidopsis. While four types of gene duplication were observed at different frequencies, whole-genome or segmental duplications were the most frequent with 162 genes, followed by 29 dispersed, 14 tandem and 4 proximal duplications, suggesting that segmental duplications contributed the most to the expansion of both gene families in flax. The rates of nonsynonymous to synonymous (Ka/Ks) mutations of paired duplicated genes were for the most part lower than one, indicative of a predominant purifying selection. Only five pairs of genes clearly exhibited positive selection with a Ka/Ks ratio greater than one. Gene ontology analyses suggested that most flax ABC transporter and HMA genes had a role in ATP binding, transport, catalytic activity, ATPase activity, and metal ion binding. The RNA-Seq analysis of eight different organs demonstrated diversified expression profiling patterns of the genes and revealed their functional or subfunctional conservation and neo-functionalization. (Continued on next page)
* Correspondence: [email protected]; [email protected] 1 Ottawa Research and Development Center, Agriculture and Agri-Food Canada, 960 Carling Avenue, Ottawa, ON K1A 0C6, Canada Full list of author information is available at the end of the article
© The Author(s). 2020 Open Access This article is licensed under a Creative Commons A
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