Integration of gene-based markers in a pearl millet genetic map for identification of candidate genes underlying drought tolerance quantitative trait loci.

Deepmala Sehgal,Vincent Vadez,Yash Pal Yadav,Ian Peter Armstead,Vengaldas Rajaram,Rattan Singh Yadav,Charles Thomas Hash

doi:10.1186/1471-2229-12-9

Abstract

BackgroundIdentification of genes underlying drought tolerance (DT) quantitative trait loci (QTLs) will facilitate understanding of molecular mechanisms of drought tolerance, and also will accelerate genetic improvement of pearl millet through marker-assisted selection. We report a map based on genes with assigned functional roles in plant adaptation to drought and other abiotic stresses and demonstrate its use in identifying candidate genes underlying a major DT-QTL.ResultsSeventy five single nucleotide polymorphism (SNP) and conserved intron spanning primer (CISP) markers were developed from available expressed sequence tags (ESTs) using four genotypes, H 77/833-2, PRLT 2/89-33, ICMR 01029 and ICMR 01004, representing parents of two mapping populations. A total of 228 SNPs were obtained from 30.5 kb sequenced region resulting in a SNP frequency of 1/134 bp. The positions of major pearl millet linkage group (LG) 2 DT-QTLs (reported from crosses H 77/833-2 × PRLT 2/89-33 and 841B × 863B) were added to the present consensus function map which identified 18 genes, coding for PSI reaction center subunit III, PHYC, actin, alanine glyoxylate aminotransferase, uridylate kinase, acyl-CoA oxidase, dipeptidyl peptidase IV, MADS-box, serine/threonine protein kinase, ubiquitin conjugating enzyme, zinc finger C- × 8-C × 5-C × 3-H type, Hd3, acetyl CoA carboxylase, chlorophyll a/b binding protein, photolyase, protein phosphatase1 regulatory subunit SDS22 and two hypothetical proteins, co-mapping in this DT-QTL interval. Many of these candidate genes were found to have significant association with QTLs of grain yield, flowering time and leaf rolling under drought stress conditions.ConclusionsWe have exploited available pearl millet EST sequences to generate a mapped resource of seventy five new gene-based markers for pearl millet and demonstrated its use in identifying candidate genes underlying a major DT-QTL in this species. The reported gene-based markers represent an important resource for identification of candidate genes for other mapped abiotic stress QTLs in pearl millet. They also provide a resource for initiating association studies using candidate genes and also for comparing the structure and function of distantly related plant genomes such as other Poaceae members.

Highlights

Identification of genes underlying drought tolerance (DT) quantitative trait loci (QTLs) will facilitate understanding of molecular mechanisms of drought tolerance, and will accelerate genetic improvement of pearl millet through marker-assisted selection
Genetic maps in pearl millet have been based on markers such as Restriction Fragment Length Polymorphism (RFLP) and Amplified Fragment Length Polymorphism (AFLP) [1,2,3,4,5] with the Simple Sequence Repeat (SSR) and Diversity Array Technolgy (DArT)-based maps [6,7,8] being in ascendancy
single nucleotide polymorphism (SNP) is available in pearl millet [44], the present study was undertaken to develop a resource of mapped genebased SNPs for pearl millet and to identify putative candidate genes underlying a major validated drought tolerance

Summary

Introduction

Identification of genes underlying drought tolerance (DT) quantitative trait loci (QTLs) will facilitate understanding of molecular mechanisms of drought tolerance, and will accelerate genetic improvement of pearl millet through marker-assisted selection. Genetic maps in pearl millet have been based on markers such as Restriction Fragment Length Polymorphism (RFLP) and Amplified Fragment Length Polymorphism (AFLP) [1,2,3,4,5] with the Simple Sequence Repeat (SSR) and Diversity Array Technolgy (DArT)-based maps [6,7,8] being in ascendancy These maps have proven useful in the identification of QTLs and breeding for drought tolerance [4,5,9], disease resistance [10,11,12,13,14] and stover quality [15] but have improved our understanding of complex relationships between the pearl millet genome and those of other graminaceous species [3]. The advantage of such markers, often described as ‘candidate gene-based’, is their close association with loci controlling variation for the trait in question, allowing the development of ‘perfect markers’ [17] that can be used for linkage disequilibrium (LD) based mapping studies [18,19] and the direct selection of genotypes with superior allele content [20]

Methods

Results

Discussion

Conclusion