Phototropism in the Marine Red Macroalga <i>Pyropia yezoensis</i>

Abstract

Phototropism is a response to the direction of light that guides growth orientation and determines the shape of plants to optimize photosynthetic activity. The phototropic response is present not only in terrestrial plants but also in water-living algae. However, knowledge about phototropism in Bangiophycean seaweeds is limited. Here, we examined the phototropic response of the red alga Pyropia yezoensis to elucidate the regulatory mechanism of phototropism in Bangiophyceae. When leafy gametophytes and filamentous sporophytes of P. yezoensis were cultured under directional light, phototropism was observed in the gametophytes. Conchosporangia on the sporophytes also exhibited phototropism. Phototropism was positive in the majority of gametophytes and conchosporangia but in some cases was negative. In addition, a strong phototropic response occurred under white light, whereas blue and red light elicited minor and no responses, respectively. This observation is in contrast with the phototropic response in terrestrial plants and several algae, in which blue light is responsible for positive phototropism. Surprisingly, the genome of P. yezoensis has no homologues of the photoreceptors for blue and red light, revealing differences in the regulation of phototropism between terrestrial plants and P. yezoensis. Studies on the phototropism in P. yezoensis could shed light on the evolutional divergence of phototropic responses in plants.

Heat-Stress Responses Differ among Species from Different ‘Bangia’ Clades of Bangiales (Rhodophyta)

“…Notably, the tip of each conchosporangium was pointed ( Figure 2 M), which is similar to the pointed conchosporangium tips of a Porphyra species collected in New Zealand [ 20 ]; however, other known Neopyropia species such as N. pseudolinearis and N. yezoensis have rounded tips [ 21 , 22 ]. Thus, as mentioned in Knight and Nelson [ 20 ], it appears that the morphology and shape of conchosporangia are effective taxonomic characteristics for discovering new species of Bangiales, although molecular validation via phylogenetic analysis would provide indispensable confirmatory evidence.…”

A unique life cycle transition in the red seaweed Pyropia yezoensis depends on apospory

“…In fact, we observed tip growth of the conchocelis (Supplementary Fig. 8) and the conchosporangium 39 , where the tip cell continually produces two cells through asymmetric cell division: an apical tip cell with proliferating activity and a neighboring differentiated vegetative cell. Thus, we propose that the tip cells in these two stages are apical stem cells and the transition from sporophyte to conchosporophyte results in a change of identity of the conchocelis stem cell to the conchosporangium stem cell, which is probably stimulated by swelling of the tip cells of the conchocelis branches.…”

Auxin Regulates Apical Stem Cell Regeneration and Tip Growth in the Marine Red Alga Neopyropia yezoensis

“…Since side branches develop from differentiated nondividing cells in conchocelis filaments (see Figure 1B of [ 47 ]), we reasoned that tip growth, with the production and maintenance of an apical stem cell, could be observed by examining the formation of a side branch from a single-celled conchocelis. Thus, we prepared single-celled conchocelis ( Figure 1 B) by chopping sporophyte filaments ( Figure 1 A) with a razor blade and examined branching from these isolated cells.…”

“…The conchosporangium, a structure representing the conchosporophyte generation of the N. yezoensis life cycle [ 40 ], is produced on the conchocelis via the swelling of the apical cell of a side branch [ 52 ], representing a type of tip growth [ 47 ]. Since nondividing differentiated cells produce side branches ( Figure S1 ), we expected that single-celled conchosporangium (as well as conchocelis) would be suitable to study tip growth.…”