Genome-Wide Association Study Reveals Novel Genes Associated with Culm Cellulose Content in Bread Wheat (Triticum aestivum, L.).

Simerjeet Kaur,Zhiwu Zhang,Amita Mohan,Sukhwinder Singh,Xu Zhang,Kulvinder S Gill,Kanwarpal S Dhugga,Prashant Vikram,Haixiao Dong,Jaswinder Singh

doi:10.3389/fpls.2017.01913

Abstract

Plant cell wall formation is a complex, coordinated and developmentally regulated process. Cellulose is the most dominant constituent of plant cell walls. Because of its paracrystalline structure, cellulose is the main determinant of mechanical strength of plant tissues. As the most abundant polysaccharide on earth, it is also the focus of cellulosic biofuel industry. To reduce culm lodging in wheat and for improved ethanol production, delineation of the variation for stem cellulose content could prove useful. We present results on the analysis of the stem cellulose content of 288 diverse wheat accessions and its genome-wide association study (GWAS). Cellulose concentration ranged from 35 to 52% (w/w). Cellulose content was normally distributed in the accessions around a mean and median of 45% (w/w). Genome-wide marker-trait association study using 21,073 SNPs helped identify nine SNPs that were associated (p < 1E-05) with cellulose content. Four strongly associated (p < 8.17E-05) SNP markers were linked to wheat unigenes, which included β-tubulin, Auxin-induced protein 5NG4, and a putative transmembrane protein of unknown function. These genes may be directly or indirectly involved in the formation of cellulose in wheat culms. GWAS results from this study have the potential for genetic manipulation of cellulose content in bread wheat and other small grain cereals to enhance culm strength and improve biofuel production.

Highlights

Increasing world population demands a sustainable increase in the production of food, feed and fuel crops (Scholey et al, 2016)
The cellulose concentration was normally distributed around the mean in the set as depicted in the density plot (Figure 1)
The minor cluster containing 20 genotypes was removed from the final analysis to account for population structure and the first PC was used as a covariate for genome-wide association study (GWAS) analyses (Figure 2)

Summary

Introduction

Increasing world population demands a sustainable increase in the production of food, feed and fuel crops (Scholey et al, 2016). Bread wheat (Triticum aestivum) occupies more agricultural area than any other food crop worldwide (http://www.wheatinitiative.org/). In addition to grain production, the annual worldwide production of wheat straw is around 3.5 × 108 tons, which is used as cattle fodder in developing countries and is a potential feedstock for cellulosic ethanol production (Singhania et al, 2014). Wheat straw, which is comprised of cellulose (∼40%), hemicelluloses (∼35%), and lignin (∼25%), is one of the most abundant lignocellulosic raw materials in the world (Ruiz et al, 2013). A paracrystalline polysaccharide, is the Genomic Association for Culm Cellulose Content main determinant of mechanical strength, which has implications in crop lodging, biotic and abiotic stresses. Cellulose amount in a unit length of the stem explains most of the variation in mechanical strength (Appenzeller et al, 2004; Dhugga, 2007). An understanding of the natural variability of cellulose in plants and its association with chromosomal regions could provide markers for enhancing grain and biomass yield (Ciesielski et al, 2014)

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Results

Discussion

Conclusion