AUTHOR=Kim Hyoung Tae , Park Sang Hee , Kim Jung Sung 

TITLE=Dynamic hybridization between two spleenworts, Asplenium incisum and Asplenium ruprechtii in Korea

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1116040

DOI=10.3389/fpls.2023.1116040

ISSN=1664-462X

ABSTRACT=<p>Natural hybridization between <italic>Asplenium incisum</italic> and <italic>A. ruprechtii</italic> has been observed in Northeast Asia and its allotetraploid species, <italic>A. castaneoviride</italic>, was reported. However, the hybridization process between the parental species and the origin of the allotetraploid taxon remains obscure. Additionally, the systematic affinities of the recently described hybrid <italic>A. bimixtum</italic>, considered to have originated from the hybridization of <italic>A. ruprechtii</italic>, <italic>A. trichomanes</italic>, and <italic>A. incisum</italic>, is unresolved owing to its similarity to <italic>A. castaneoviride</italic>. The goals of this study were to (1) investigate the hybridization between <italic>A. ruprechtii</italic> and <italic>A. incisum</italic>; (2) verify the origin of <italic>A. castaneoviride</italic> occurring in Korea, whether it independently arose from 2x sterile hybrids; and (3) elucidate the reliability of identifying <italic>A. bimixtum</italic>. Three genotypes, <italic>A. incisum</italic>, <italic>A. ruprechtii</italic>, and their hybrid, were identified based on the nuclear gene <italic>pgiC</italic> sequence and finally divided them into six types by ploidy levels: diploid <italic>A. incisum</italic>, <italic>A. ruprechtii</italic>, and four hybrid types (diploid <italic>A. × castaneoviride</italic>, triploid <italic>A. × castaneoviride</italic>, allotetraploid <italic>A. castaneoviride</italic>, and <italic>A. bimixtum</italic>). In the analyses of plastid DNA, all hybrids had an <italic>A. ruprechtii</italic>-type <italic>rbcL</italic> gene. In addition, the four plastomes of <italic>A. ruprechtii</italic> and the hybrids had high pairwise sequence identities greater than 98.48%. They increased up to 99.88% when a large deletion of <italic>A.</italic> x <italic>castaneoriviride</italic> (2x) collected from Buramsan populations was ignored. Notably, this large deletion was also found in triploid <italic>A. × castaneoviride</italic> and allotetraploid <italic>A. castaneoviride</italic> in the same populations. Sequence data of the nuclear and plastid genes showed that hybridization is unidirectional, and <italic>A. ruprechtii</italic> is the maternal parent. The large deletion of <italic>rpoC2-rps2</italic> commonly found in the different ploidy hybrids of the Buramsan population suggests that the allotetraploid <italic>A. castaneoviride</italic> can be created independently from sterile hybrids. We assume that both polyploidization driving allopolyploidy and minority cytotype exclusion took place independently in the population, since <italic>A castaenoviride</italic> co-occurs with <italic>A. ruprechtii</italic> in small populations. Furthermore, it was also observed that an enlarged noncoding region in fern organelle (ENRIFO) of the plastome was found in the genus <italic>Asplenium</italic>.</p>