Lack of ITS sequence homogenization in Erysimum species (Brassicaceae) with different ploidy levels

Funding This research is supported by grants from FEDER/Junta de Andalucía-Consejería de Economía y Conocimiento A-RNM-505-UGR18 and P18-FR-3641. This research was also funded by the Spanish Ministry of Science and Innovation (CGL2013-47558-P and PID2021-126456NB-C22), including EU FEDER funds. COM was supported by the Ministry of Economy and Competitiveness (BES-2014-069022). This is a contribution to the Research Unit Modeling Nature, funded by the Consejería de Economía, Conocimiento, Empresas y Universidad, and European Regional Development Fund (ERDF), reference QUALIFICA 00011.Acknowledgements The authors thank the Tatiana López Pérez and the Evoflor group for helping us during several phases of the study. We also thank the Sierra Nevada National Park headquarters for providing access to sampling in the National Park.The internal transcribed spacers (ITS) exhibit concerted evolution by the fast homogenization of these sequences at the intragenomic level. However, the rate and extension of this process are unclear and might be conditioned by the number and divergence of the different ITS copies. In some cases, such as hybrid species and polyploids, ITS sequence homogenization appears incomplete, resulting in multiple haplotypes within the same organism. Here, we studied the dynamics of concerted evolution in 85 individuals of seven plant species of the genus Erysimum (Brassicaceae) with multiple ploidy levels. We estimated the rate of concerted evolution and the degree of sequence homogenization separately for ITS1 and ITS2 and whether these varied with ploidy. Our results showed incomplete sequence homogenization, especially for polyploid samples, indicating a lack of concerted evolution in these taxa. Homogenization was usually higher in ITS2 than in ITS1, suggesting that concerted evolution operates more efficiently on the former. Furthermore, the hybrid origin of several species appears to contribute to the maintenance of high haplotype diversity, regardless of the level of ploidy. These findings indicate that sequence homogenization of ITS is a dynamic and complex process that might result in varying intra- and inter-genomic diversity levels.FEDER/Junta de Andalucía-Consejería de Economía y Conocimiento A-RNM-505-UGR18 and P18-FR-3641Spanish Ministry of Science and Innovation (CGL2013-47558-P and PID2021-126456NB-C22)Ministry of Economy and Competitiveness (BES-2014-069022)Research Unit Modeling Nature, funded by the Consejería de Economía, Conocimiento, Empresas y Universidad, and European Regional Development Fund (ERDF), reference QUALIFICA 0001