Background Gene duplication is a prevalent phenomenon and a major driving force underlying genome evolution. The process leading to the fixation of gene duplicates following duplication is critical to understand how genome evolves but remains fragmentally understood. Most previous studies on gene retention are based on gene duplicate analyses in single reference genome. No population-based comparative gene retention analysis has been performed to date. Results Taking advantage of recently published genomic data in Triticeae, we dissected a divergent homogentisate phytyltransferase (HPT2) lineage caught in the middle stage of gene fixation following duplication. The presence/absence of HPT2 in barley (diploid), wild emmer (tetraploid), and bread wheat (hexaploid) pangenome lines appears to be associated with gene dosage constraint and environmental adaption. Based on these observations, we adopted a phylogeny-based orthology inference approach and performed comparative gene retention analyses across barley, wild emmer, and bread wheat. This led to the identification of 326 HPT2-pattern-like genes at whole genome scale, representing a pool of gene duplicates in the middle stage of gene fixation. Majority of these HPT2-pattern-like genes were identified as small-scale duplicates, such as dispersed, tandem, and proximal duplications. Natural selection analyses showed that HPT2-pattern-like genes have experienced relaxed selection pressure, which is generally accompanied with partial positive selection and transcriptional divergence. Functional enrichment analyses showed that HPT2-pattern-like genes are over-represented with molecular-binding and defense response functions, supporting the potential role of environmental adaption during gene retention. We also observed that gene duplicates from larger gene family are more likely to be lost, implying a gene dosage constraint effect. Further comparative gene retention analysis in barley and bread wheat pangenome lines revealed combined effects of species-specific selection and gene dosage constraint. Conclusions Comparative gene retention analyses at the population level support gene dosage constraint, environmental adaption, and species-specific selection as three factors that may affect gene retention following gene duplication. Our findings shed light on the evolutionary process leading to the retention of newly formed gene duplicates and will greatly improve our understanding on genome evolution via duplication.
Key message A major grain length QTL on chromosome 2H was fine mapped to a 140.9 Kb region containing three genes. Abstract Increasing yield is an important target for barley breeding programs. One approach to increase yield is by enhancing individual grain weights through the regulation of grain size. Fine mapping major grain size-related quantitative trait loci is necessary for future marker-assisted selection strategies, yet studies of this nature are limited in barley. In the present study, we utilised a doubled haploid population derived from two Australian malt barley varieties, Vlamingh and Buloke, coupled with extensive genotypic and phenotypic data from three independent environments. A major grain length locus identified on chromosome 2H designated qGL2H was fine mapped to a 140.9 Kb interval. qGL2H was able to account for 25.4% of the phenotypic variation for grain length and 10.2% for grain yield. Underlying qGL2H were three high-confidence predicted genes. One of these genes encodes a MYB transcription factor and represents a promising candidate for further genetic research.
Predicted climate change is widely cited to significantly reduce yields of the major cereal crop species in a period where demand is rapidly rising due to a growing global population. This requires exhaustive research to develop genetic resources in order to address the expected production deficiencies which will largely be driven by abiotic stress. Modification of multiple genes is an approach that can address the predicted challenges; however, it is time-consuming and costly to modify multiple genes simultaneously. Transcription factors represent a group of proteins regulating multiple genes simultaneously and are therefore promising targets to concurrently improve multiple traits concurrently, such as abiotic stress tolerance and grain size (a contributor to yield). Many studies have identified the complex role that transcription factors of multiple families have contributed toward abiotic stress tolerance or grain size, although research addressing both simultaneously is in its infancy despite its potential significance for cereal crop improvement. Here we discuss the potential role that transcription factors may contribute toward improving cereal crop productivity under adverse environmental conditions and offer research objectives that need to be addressed before the modification of transcription factors becomes routinely used to positively manipulate multiple target traits.
MYB transcription factors (TFs) represents one of the largest TF families in plants. In this study, we performed genome-wide MYB-domain screening and identified a total of 997 MYBs in wheat (Triticum aestivum), among which 445 were 2-domain MYBs (R2R3-MYBs) that were clustered into 15 subgroups with varied conservation profiles. Homologous genes were highly conserved across the three subgenomes, with minor variations contributed by segmental duplications. Tandem and proximal gene duplications have contributed significantly to the expansion of the wheat Myb gene family. Furthermore, comprehensive transcriptome profiling of R2R3-Myb genes in 61 different tissue and time point samples revealed a clear pattern of temporal and spatial variations within six expression groups. The comprehensive genomic and transcriptional analyses provided valuable insights into the evolution and biological functions of R2R3-Myb genes in wheat. They would serve as a useful guide to further investigate the potential agronomic traits controlled by this large TF family.
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