Elsevier

Plant Science

Volume 173, Issue 3, September 2007, Pages 327-339
Plant Science

Comparative transcriptome analysis of salt-tolerant wheat germplasm lines using wheat genome arrays

https://doi.org/10.1016/j.plantsci.2007.06.005Get rights and content

Abstract

Salt-tolerant wheat lines W4909 and W4910 were derived from a cross between AJDAj5 (a disomic addition line carrying a pair of Eb chromosomes from Thinopyrum junceum) and PhI (a line having the PhI allele from Aegilops speltoides, which promotes homoeologous recombination). Both lines have greater salt tolerance than their parental lines, which are more salt-tolerant than the common wheat background, Chinese Spring (CS). Genomic constitution of W4909 and W4910 wheat has been estimated at 1.9% and 2.4% non-CS, respectively. Affymetrix GeneChip® Wheat Arrays were used to identify differentially expressed genes in roots and leaves of the above-mentioned five lines under salt stress at electrical conductivity (EC) of 30 dS/m. Based on expression polymorphisms in AJDAj5 and PhI, differentially expressed genes in W4909 and W4910 were attributed to one or the other parental lines when possible. The PhI parent contributed nearly twice as many expression polymorphisms as AJDAj5 to both W4909 and W4910. Nine transcripts in W4910 showed transgression gene expression significantly higher or lower than either parent. The majority of expression polymorphisms exhibited very low expression levels compared to the control and mapped to three distinct chromosomal locations, 2S, 4L and 2L. Salt treatment responsive gene expression profiles common to all five tested lines provide a short list of candidate salt-tolerance genes in wheat. A gene for tonoplast aquaporin that was transferred from PhI and a gene for putative potassium channel protein that was attributable to AJDAj5 are identified as candidate genes for the tissue salt tolerance in W4909 and W4910.

Introduction

Abiotic stresses such as drought, salinity, and temperature have been shown to reduce average crop yield by more than 50% with yield losses for wheat as great as 80% [1]. It is estimated that 20–30% of the world's irrigated soil is adversely affected by salinity [2], [3]. Salt stress in plants is due primarily to ion cytotoxicity involving alteration of cytosolic K+/Na+ ratios and osmotic stress that disrupts homeostasis and ion distribution in the cell [4], [5] leading to denaturation of structural and functional proteins [6].

Plants survive in saline soils by excluding Na+ at the plasma membrane [4], [7], [8], sequestering Na+ in intracellular vacuoles [9], [10], and accumulation of osmolites and osmoprotectants [11]. The end result of these mechanisms is proper K+/Na+ ratios and correct cellular osmolarity. Varieties of barley and tomato exhibit high variations in salt tolerance [12], which suggests that mutations exist in functional or regulatory genes that can confer salt tolerance on salt-sensitive plants [3]. However, wild annual and perennial wheatgrasses have even greater salt tolerance than cultivated crops [13], [14], [15].

Two salinity-tolerant wheat recombinant lines, W4909 and W4910 [16], were generated by crossing a wheat disomic addition line AJDAj5, which harbors a pair of Thinopyrum junceum Eb chromosomes [17], with the Aegilops speltoides derived Ph inhibitor line PhI [18] that promotes homoeologous recombination. W4909 and W4910 have been estimated to be genetically different from Chinese Spring by 1.9% and 2.4%, respectively, using AFLP markers [16]. Both lines have greater salt tolerance than either parent (AJDAj5 and PhI), which have greater tolerance than the Chinese Spring background [16]. We hypothesize that some genes that are transferred from the AJDAj5 and PhI parents contribute to the enhanced salt tolerance in the recombinant lines. In this study we utilized microarray analysis to assess the gene expression differences in these lines, measure the contribution of AJDAj5 and PhI to each line, and identify expression polymorphisms unique to salt tolerant W4909 and W4910 with respect to the more salt-sensitive Chinese Spring. We report here the results of transcriptome analysis of W4909, W4910, the parental lines AJDAj5 and PhI, and the common background Chinese Spring under salt stress conditions.

Section snippets

Plant materials

Wheat plants representing germplasm lines W4909 and W4910 [16], AJDAj5 [17], PhI [18], and cv. Chinese Spring were grown in a greenhouse under natural light from mid-March through mid-April with diurnal temperature range of 60–85 °F at the USDA-ARS Forage and Range Research Laboratory in Logan, Utah. Plants were grown in 70-grain silica sand with one plant per Cone-tainer1

Identification of expression polymorphisms in salt-stressed W4909 and W4910 wheat germplasm and their parental lines

Wheat germplasm lines W4909 and W4910 are more salt tolerant than either of their parental lines AJDAj5 and PhI [16]. Microarray analysis was used to identify differentially expressed genes in roots and shoots and determine the parental contribution to enhanced salt tolerance in these lines. Significantly different (greater than 2-fold) patterns of transcript expression that were attributable to one or the other parental lines were identified as expression level polymorphisms (ELPs) and are

Acknowledgments

This research is supported by USDA-ARS Administrator's Postdoctoral Research Associate Program, 2003 class.

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