A study of solid-stem expression in durum and common wheat
Date
2018-01-24
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0002-9477-5549
Type
Thesis
Degree Level
Doctoral
Abstract
The wheat stem sawfly (WSS) is a damaging insect pest of wheat in North America. Resistance to WSS has primarily been achieved by introgressing the stem-solidness QTL SSt1 into elite cultivars. This thesis comprehensively examined the expression of SSt1 from both the phenotypic and genetic perspective. The first study investigated the influence of four sowing densities on pith expression for two newly released solid-stemmed durum cultivars, CDC Fortitude and AAC Raymore. Both cultivars had strong pith expression (average stem-solidness > 3.9) across all environments and sowing densities, in contrast to the common wheat cultivar Lillian (average stem-solidness = 2.2). Increasing sowing density had a positive effect on grain yield in all cultivars, but was negatively associated with stem-solidness. These findings suggest that, unlike with Lillian, altering sowing density is not required to achieve effective sawfly resistance with CDC Fortitude and AAC Raymore. For the second study, we improved the resolution of the SSt1 interval in durum and common wheat by localizing coincident QTL near the telomere of 3BL (LOD = 94 - 127, R2 = 78 - 92 %). The SSt1 interval spanned a 1.6 Mb interval on chromosome 3B. Minor QTL were identified on chromosomes 2A, 2D, 4A, and 5A that synergistically enhanced the expression of SSt1 to increase stem-solidness. These results suggest breeding for improved stem-solidness is possible by combining SSt1 with favorable alleles at minor loci. Finally, we investigated gene expression and structural variation within the SSt1 interval. This showed that in addition to structural variation between genome assemblies, the SSt1 locus has also undergone a series of functional gene duplication/expansion events. One gene encoding a Dof transcription factor (TraesCS3B01G60880) was consistently up-regulated across solid-stemmed cultivars. Further investigation revealed that solid-stemmed cultivars carry multiple copies of TraesCS3B01G60880. Screening of a mutant population identified two mutant lines with a hollow-stemmed phenotype that either have a deletion, or reduced expression of TraesCS3B01G60880. Taken together, this research provides new insights into the phenotypic and genetic expression of SSt1 in wheat, and will provide an important foundation for future experiments that will help breeders improve resistance to the WSS.
Description
Keywords
Wheat Stem Sawfly, Wheat, RNAseq, Gene Expression, 90K, High Density Mapping, Stem-Solidness, Comparative Genomics, QTL Mapping
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Plant Sciences
Program
Plant Science