Gene Family Evolution in Allium Species

Abstract

During evolution, plant genomes have undergone duplications, deletions and rearrangements resulting in a wide variation in genome size and number of gene family members between different species. The variation in gene families is an important mechanism for adaptation to different environmental conditions. Allium species, such as bulb onion (Allium cepa), have a large unsequenced genome. However, high throughput transcriptome sequencing datasets are now available which provide an efficient way to identify the genes present in different Allium species. With this knowledge, strategies to accelerate physiological and genetic analysis for enhanced breeding can be developed. In this chapter, we will describe how RNA sequencing is providing a better understanding of Allium genetics and survey the diversity of gene families involved in bulbing, flowering, male fertility, flavonoid biosynthesis and sulphur assimilation in bulb onion. In general, we found that onion has a similar number of gene family members to other monocots, such as rice, which have much smaller genomes. This is consistent with the large genome size of Allium being due to a massive expansion of repetitive DNA.