Evidence for newly discovered albino mutants in a pyroloid: implication for the nutritional mode in the genus Pyrola

Abstract

Premise: Difficulties in comparing extremely divergent features in fully mycoheterotrophic plants with those in closely related chlorophyllous plants have complicated attempts to reveal the evolutionary patterns and processes of fully mycoheterotrophic plants. Albino mutants of partially mycoheterotrophic plants, generally observed in Orchidaceae, have provided an ideal model for investigating the evolution of mycoheterotrophy within similar genetic backgrounds. In 2018, we found a putative albino population of Pyrola (Ericaceae). Here we aimed to reveal the identity of the albino pyroloid and confirm its fully mycoheterotrophic status.

Methods: To reveal the putative albino pyroloid's identity, we examined its morphology and sequenced its chloroplast DNA. In addition, we assessed the trophic status of the putative albino pyroloid by analyzing chlorophyll fluorescence, chlorophyll concentration, and natural ¹³ C and ¹⁵ N abundances.

Results: We identified albino individuals as P. japonica-otherwise a partially mycoheterotrophic species. We confirmed their albino status by their considerably lower chlorophyll fluorescence and concentrations than those of sympatrically occurring chlorophyllous plants. ¹³ C abundance in the albino individuals was significantly higher than in the green individuals of P. japonica.

Conclusions: This first report of albino mutants from partially mycoheterotrophic species in angiosperms other than orchids will play a valuable role in further studies focused on mycoheterotrophy. For instance, their δ¹³ C and δ¹⁵ N values represent a reference for fully mycoheterotrophic plants in Pyrola. Our findings also indicate the strong dependence of some leafy Pyrola species on fungal C during their entire life cycle.

Keywords: Chimaphila; Pyrola aphylla; Pyrola subaphylla; Ericaceae; Japan; Pyrola japonica species complex; flora; mixotrophy; stable isotope.

Figure 1

Albino mutants of Pyrola japonica at Sapporo‐shi, Hokkaido, Japan on 18 July 2018. A, Habit; B, flower; C, developed leaf; D, young fruits; E, roots; F, habitat. Scale bars = 2 cm.

Figure 2

Abundance of δ ¹³C and δ ¹⁵N in a population of Pyrola japonica albino mutants. Black square, albino mutants (leaf); black circle, albino mutants (flower); gray square, wild‐type P. japonica (leaf); gray circle, wild‐type P. japonica (flower); white triangle, Chimaphila japonica (leaf); white rhombus, autotrophic reference plants (leaf). Plots, error bars, and dashed gray lines indicate, respectively, mean value, standard deviation (n > 2), and mean δ ¹³C and δ ¹⁵N values of autotrophic reference plants.