The plasticity of NBS resistance genes in sorghum is driven by multiple evolutionary processes.

Emma Mace,Wushu Hu,David Innes,Shuaishuai Tai,Jun Wang,David Jordan,Peter Prentis,Bradley Campbell,Alan Cruickshank,Ian Godwin,Edward Gilding

doi:10.1186/s12870-014-0253-z

Abstract

BackgroundIncreased disease resistance is a key target of cereal breeding programs, with disease outbreaks continuing to threaten global food production, particularly in Africa. Of the disease resistance gene families, the nucleotide-binding site plus leucine-rich repeat (NBS-LRR) family is the most prevalent and ancient and is also one of the largest gene families known in plants. The sequence diversity in NBS-encoding genes was explored in sorghum, a critical food staple in Africa, with comparisons to rice and maize and with comparisons to fungal pathogen resistance QTL.ResultsIn sorghum, NBS-encoding genes had significantly higher diversity in comparison to non NBS-encoding genes and were significantly enriched in regions of the genome under purifying and balancing selection, both through domestication and improvement. Ancestral genes, pre-dating species divergence, were more abundant in regions with signatures of selection than in regions not under selection. Sorghum NBS-encoding genes were also significantly enriched in the regions of the genome containing fungal pathogen disease resistance QTL; with the diversity of the NBS-encoding genes influenced by the type of co-locating biotic stress resistance QTL.ConclusionsNBS-encoding genes are under strong selection pressure in sorghum, through the contrasting evolutionary processes of purifying and balancing selection. Such contrasting evolutionary processes have impacted ancestral genes more than species-specific genes. Fungal disease resistance hot-spots in the genome, with resistance against multiple pathogens, provides further insight into the mechanisms that cereals use in the “arms race” with rapidly evolving pathogens in addition to providing plant breeders with selection targets for fast-tracking the development of high performing varieties with more durable pathogen resistance.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0253-z) contains supplementary material, which is available to authorized users.

Highlights

Increased disease resistance is a key target of cereal breeding programs, with disease outbreaks continuing to threaten global food production, in Africa
The nucleotide-binding site (NBS)-encoding genes were significantly enriched in the regions of the genome containing fungal pathogen disease resistance Quantitative trait loci (QTL) (Χ2 p-value 0.00272)
This study, focusing on the most prevalent and ancient of the disease resistance gene families, has presented new data demonstrating that NBS-encoding genes are under strong selection pressure in sorghum, through the contrasting evolutionary processes of purifying and balancing selection, and that they are enriched in the regions of the genome associated with fungal pathogen disease resistance

Summary

Introduction

Increased disease resistance is a key target of cereal breeding programs, with disease outbreaks continuing to threaten global food production, in Africa. Of the disease resistance gene families, the nucleotide-binding site plus leucine-rich repeat (NBS-LRR) family is the most prevalent and ancient and is one of the largest gene families known in plants. Among all disease resistance genes, the nucleotidebinding site plus leucine-rich repeat genes (NBS-LRR) are the most prevalent and ancient and are one of the largest gene families known in plants [5]. These genes are involved in the detection and response to diverse pathogens, including bacteria, viruses, fungi, nematodes, insects and oomycetes [5]. NBS-LRR genes encode an N-terminal variable domain, a central nucleotide-binding site (NBS)

Methods

Results

Discussion

Conclusion