Evaluating the spore genome sizes of ferns and lycophytes: a flow cytometry approach

Abstract

Ferns and lycophytes produce spores to initiate the gametophyte stage for sexual reproduction. Approximately 10% of these seedless vascular plants are apomictic, and produce genomic unreduced spores. Genome size comparisons between spores and leaves are a reliable, and potentially easier way to determine their reproductive mode compared to traditional approaches. However, estimation of the spore genome sizes of these plants has not been attempted. We attempted to evaluate the spore genome sizes of ferns and lycophytes using flow cytometry, collected spores from selected species representing different spore physical properties and taxonomic groups, and sought to optimize bead-vortexing conditions. By evaluating the spore and sporophyte genome sizes, we examined whether reproductive modes could be ascertained from these flow cytometry results. We proposed two separate sets of optimized bead-vortexing conditions for the nuclear extraction of green and nongreen spores. We further successfully extracted spore nuclei of 19 families covering most orders, and the qualities and quantities of these extractions satisfied the C-value criteria. These evaluated genome sizes further supported the reproductive modes reported previously. In the current study, flow cytometry was used for the first time to evaluate the spore genome sizes of ferns and lycophytes. This use of spore flow cytometry provides a new, efficient approach to ascertaining the reproductive modes of these plants.

Pure polyploidy: Closing the gaps in autopolyploid research

“…In ferns, unreduced spore production has been inferred (Gastony, ), and even used experimentally (Rabe & Haufler, ), as a pathway to WGD. Like angiosperm pollen, fern spores are easily isolated, and both mega‐ and microspores in heterosporous ferns and the single spore type in homosporous ferns can be assayed for meiotic nonreduction directly through flow cytometry (Kuo et al, ) or indirectly through flow cytometry of gametophytes following spore germination. Analyzing genome size in both spores and gametophytes from the same set of individuals would comprise a simple way to estimate both unreduced spore formation and the relative viability of unreduced gametophytes.…”

Phylogenetic analyses place the monotypic Dryopolystichum within Lomariopsidaceae

“…The genome sizes of spore and leaf nuclei of SITW10443 were examined by flow cytometry in order to infer the reproductive mode (Kuo et al 2017). The genome size of spore nuclei should be half the genome size of leaf nuclei in the case of sexual and the same size in the case of apomictic reproduction (Kuo et al 2017).…”

“…The genome size of spore nuclei should be half the genome size of leaf nuclei in the case of sexual and the same size in the case of apomictic reproduction (Kuo et al 2017). We followed Kuo et al (2017) for the extraction of leaf nuclei.…”

“…The genome size of spore nuclei should be half the genome size of leaf nuclei in the case of sexual and the same size in the case of apomictic reproduction (Kuo et al 2017). We followed Kuo et al (2017) for the extraction of leaf nuclei. For extraction of spore nuclei, we used an optimized bead-vortexing treatment with vertex duration of 1 minute and vertex speed of 1,900 rpm, as described by Kuo et al (2017).…”

“…We followed Kuo et al (2017) for the extraction of leaf nuclei. For extraction of spore nuclei, we used an optimized bead-vortexing treatment with vertex duration of 1 minute and vertex speed of 1,900 rpm, as described by Kuo et al (2017). An external standard was not necessary since we only need to compare the two phases of the life-cycle to each other.…”