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Polyglutamine and Polyalanine Tracts Are Enriched in Transcription Factors of Plants

Polyglutamine (polyQ) tracts have been studied extensively for their roles in a number of human diseases such as Huntington's or different Ataxias. However, it has also been recognized that polyQ tracts are abundant and may have important functional and evolutionary roles. Especially the association of polyQ and also polyalanine (polyA) tracts with transcription factors and their activation activity has been noted. While a number of examples for this association have been found for proteins from opisthokonts (animals and fungi), only a few studies exist for polyQ and polyA stretches in plants, and systematic investigations of the significance of these repeats in plant transcription factors are scarce. Here, we analyze the abundance and length of polyQ and polyA stretches in the conceptual proteomes of six plant species and examine the connection between polyQ and polyA tracts and transcription factors of the repeat-containing proteins. We show that there is an association of polyQ stretches with transcription factors in plants. In grasses, transcription factors are also significantly enriched in polyA stretches. While there is variation in the abundance, length, and association with certain functions of polyQ and polyA stretches between different species, no general differences in the evolution of these repeats could be observed between plants and opisthokonts.