Dominikia litorea, Blaszk. & Kozlowska, 2018

Błaszkowski, Janusz, Ryszka, Przemysław & Kozłowska, Anna, 2018, Dominikia litorea, a new species in the Glomeromycotina, and biogeographic distribution of Dominikia, Phytotaxa 338 (3), pp. 241-254 : 247-252

Dominikia litorea

The most peculiar morphological character of D. litorea is the equal thickness of its two spore wall layers (Fig. 3B‒H). The dextrinoid reaction of spore wall layer 2, which appears in most spores mounted in Melzer’s reagent, also distinguishes the new species (Fig. 3C‒E, G, H). In addition, the facts that D. litorea forms spores only in clusters and the spores remain hyaline regardless of age are noteworthy.

Of the 12 previously described Dominikia spp. , only D. indica and D. minuta produce spores that remain hyaline throughout their entire life cycle and the spores have a spore wall consisting of two layers ( Błaszkowski et al. 2000, 2010b).

However, most importantly, although spore wall layer 1 of D. litorea and D. indica is similar in thickness, in the former species it is permanent and nonreactive in Melzer’s reagent (Fig. 3C, E, G, H), and in the latter fungus layer 1 is short-lived, usually completely sloughed off in mature spores, and it stains pinkish (11A2) to pink (12A4) in Melzer’s ( Błaszkowski et al. 2010b). In both species, spore wall layer 2 is laminate, but in D. litorea it is 1.5‒3.3-fold thinner and usually shows dextrinoid properties in Melzer’s reagent (Fig. 3‒E, G, H); in D. indica it remains nonreactive in this reagent. In addition, in comparison to D. indica , at the spore base the spore subtending hypha of D. litorea is 1.2‒1.6-fold narrower, has a 1.6‒2.0-fold thinner wall and a 1.1‒1.4-fold narrower pore, which rarely is closed by a septum continuous with some innermost laminae of spore wall layer 2; in D. litorea no such a septum was observed (Fig. 3C‒H).

Morphologically, D. litorea and D. minuta differ significantly and the differences mainly regard some of the phenotypic and histochemical features of components of the spore wall ( Błaszkowski et al. 2000). In both species, spore wall layers 1 and 2 are permanent and of the same types: uniform and laminate, respectively. However, the spore wall of D. litorea is 1.3‒2.3-fold thicker than that of D. minuta , despite the laminate spore wall layer 2 in both species is similar in thickness. Spore wall layer 1 of D. minuta measures only 0.2‒0.7 μm, thus it is 1.7‒4.0-fold thinner than in D. litorea . Moreover, spore wall layer 1 of D. minuta frequently swells in PVLG and easily cracks in mature spores following their crushing. In D. litorea , spore wall layer 1 never swells in PVLG and is not fragile (Fig. 3B‒H). Histochemically, D. minuta is distinguished by the lack of any reaction of its spore wall layers in Melzer’s reagent, whereas spore wall layer 2 of D. litorea usually stains in this reagent (Fig. 3C‒E, G, H). Finally, D. minuta frequently produces single spores, whereas those of D. litorea occur only in clusters (Fig. 3A).

The clear morphological separateness of D. litorea relative to the other known Dominikia spp. discussed above much more and unambiguously confirmed phylogenetic analyses of sequences of the SSU‒ITS‒LSU nrDNA region and the RPB1 gene ( Figs 1 , 2 ). The analyses generated trees, in which D. litorea was placed basally relatively to all but D. indica ( Fig. 1 ) or all previously described Dominikia spp. ( Fig. 2 ) and showed a large molecular distance between D. litorea and the other species of the genus (see General data and phylogeny).

Figure 3. Dominikia litorea spores. A. Intact spores in cluster. B‒E. Spore wall layers (swl) 1 and 2 of the same thickness and easily separating from each other; note the presence of soil debris in the spore clusters showed in Fig. 3D and E. F. Spore wall layers (swl) 1 and 2 and funnel-shaped subtending hypha (sh). G, H. Spore wall layers (swl) 1 and 2 continuous with subtending hyphal wall layers (shwl) 1 and 2. A, B. Spores in PVLG. C‒H. Spores in PVLG+Melzer’s reagent. A‒H. Differential interference microscopy. Bars: A‒H = 10 μm

*N – no available data, M – identified by morphological analyses, MA – identified by molecular analyses, ES – identified based on the environmental sequence(s) showed

The biogeographic data presented in this paper (see above) convincingly prove that AMF of the genus Dominikia are widely distributed on Earth and probably coexist with a wide range of plant species growing in habitats of extremely different abiotic and biotic environmental conditions ( Table 1).

No studies have been performed on the influence of Dominikia spp. on plants and plant communities with which they are associated, and ecosystems in which they exist. Their abundant sporulation even in very old (15 years) trap and single-species cultures (Błaszkowski, pers. observ.) indicate that they are persistent microorganisms, despite their extraradical structures (spores and hyphae) quickly undergo decomposition in the field. The persistence is certainly provided by protective structures of roots, in which the fungi frequently form abundant assemblages of spores and hypha (Błaszkowski 2012, Błaszkowski et al. 2009, 2010a, 2015a). The large number of spores produced in extraradical clusters by most Dominikia spp. also suggests that the colonization power of the fungi is very high. Thus, the fungi with a lot of confidence play an important role in establishing, shaping, and functioning of single plants and plant communities. In order to confirm the suppositions presented above and use Dominikia spp. in practice, for example, in protection of dune plants and ecosystems, where most species of the genus have been discovered, appropriately targeted studies should be performed. Such studies should not be difficult due to technical problems because all of the Dominikia spp. known to date have been easy to grow in sand cultures (Błaszkowski pers. observ. and comm.). An open question is whether they can be grown equally well in in vitro cultures.

Figures

FIGURE 1. A 50% majority rule consensus phylogram inferred from a Bayesian analysis of SSU‒ITS‒LSU nrDNA sequences of Dominikia litorea, 17 other known species of AMF, an undescribed Dominikia 211, and Claroideoglomus claroideum as outgroup. The new species is in boldface and is followed by its GenBank accession numbers. The Bayesian posterior probabilities ≥0.50 and ML bootstrap values ≥50% are shown near the branches, respectively. Bar indicates 0.1 expected change per site per branch.

FIGURE 2. A 50% majority rule consensus phylogram inferred from a Bayesian analysis of RPB1 sequences of Dominikia litorea, 11 other known species of AMF, and Claroideoglomus claroideum as outgroup. The new species is in boldface and is followed by its GenBank accession numbers. The Bayesian posterior probabilities ≥0.50 and ML bootstrap values ≥50% are shown near the branches, respectively. Bar indicates 0.1 expected change per site per branch.