Abstract
Duckweeds represent a small, free-floating aquatic family (Lemnaceae) of the monocot order Alismatales with the fastest growth rate among flowering plants. They comprise five genera (Spirodela, Landoltia, Lemna, Wolffiella, and Wolffia) varying in genome size and chromosome number. Spirodela polyrhiza had the first sequenced duckweed genome. Cytogenetic maps are available for both species of the genus Spirodela (S. polyrhiza and S. intermedia). However, elucidation of chromosome homeology and evolutionary chromosome rearrangements by cross-FISH using Spirodela BAC probes to species of other duckweed genera has not been successful so far. We investigated the potential of chromosome-specific oligo-FISH probes to address these topics. We designed oligo-FISH probes specific for one S. intermedia and one S. polyrhiza chromosome (Fig. 1a). Our results show that these oligo-probes cross-hybridize with the homeologous regions of the other congeneric species, but are not suitable to uncover chromosomal homeology across duckweeds genera. This is most likely due to too low sequence similarity between the investigated genera and/or too low probe density on the target genomes. Finally, we suggest genus-specific design of oligo-probes to elucidate chromosome evolution across duckweed genera.
Highlights
Duckweeds comprise together 36 species within five genera: Spirodela (2), Landoltia (1), Lemna (12), Wolffiella (10), and Wolffia (11)
A set of 27,116 probes was designed to cover the first 7.79 Mb of S. intermedia ChrSi09 (Si09:1-7790000, referred to as ChrSi09beg) and to maintain cross-hybridization capabilities with S. polyrhiza ChrSp08. Another set of 13,682 probes was designed against the rest of ChrSi09 (Si09:779000012648911, referred to as ChrSi09end), maintaining crosshybridization capabilities with S. polyrhiza ChrSp18
A set of 13,696 probes was designed to cover the entire S. polyrhiza ChrSp19 (ChrSp19:1-3959484) with the ability to hybridize to S. intermedia ChrSi17
Summary
Duckweeds comprise together 36 species within five genera: Spirodela (2), Landoltia (1), Lemna (12), Wolffiella (10), and Wolffia (11). From the ancient genus Spirodela towards the most derived genus Wolffia, organismic complexity (many roots versus no roots) and size (1.5 cm to less than 1 mm in diameter), genome size (from 160 Mbp to 2.2 Gbp), and chromosome number vary considerably within and between genera (Landolt 1986; Wang et al 2011; Hoang et al 2019). Because of these features, duckweeds are an interesting subject for physiological, developmental and evolutionary studies. Cytogenetic maps, based on chromosomal localization of ~ 100
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