Different Growth and Sporulation Responses to Temperature Gradient among Obligate Apomictic Strains of Ulva prolifera.

Yoichi Sato,Yutaro Kinoshita,Miho Mogamiya,Masanori Hiraoka,Masakazu Hoshino,Eri Inomata

doi:10.3390/plants10112256

Abstract

The green macroalga Ulva prolifera has a number of variants, some of which are asexual (independent from sexual variants). Although it has been harvested for food, the yield is decreasing. To meet market demand, developing elite cultivars is required. The present study investigated the genetic stability of asexual variants, genotype (hsp90 gene sequences) and phenotype variations across a temperature gradient (10–30 °C) in an apomictic population. Asexual variants were collected from six localities in Japan and were isolated as an unialgal strain. The hsp90 gene sequences of six strains were different and each strain included multiple distinct alleles, suggesting that the strains were diploid and heterozygous. The responses of growth and sporulation versus temperature differed among strains. Differences in thermosensitivity among strains could be interpreted as the result of evolution and processes of adaptation to site-specific environmental conditions. Although carbon content did not differ among strains and cultivation temperatures, nitrogen content tended to increase at higher temperatures and there were differences among strains. A wide variety of asexual variants stably reproducing clonally would be advantageous in selecting elite cultivars for long-term cultivation. Using asexual variants as available resources for elite cultivars provides potential support for increasing the productivity of U. prolifera.

Highlights

Bio-Resources Business Development Division, Riken Food Co., Ltd., Miyagi 985-0844, Japan; Nishina Center for Accelerator-Based Science, RIKEN, Saitama 351-0198, Japan
The hsp90 gene sequences of the six strains showed the presence of alternative bases at some positions, indicating the presence of different alleles (Figure 1) and suggesting that these strains are heterozygous and diploid
Previous studies did not did not identify the generation or type of life cycle of the specimens used in culture identify the generation or type of life cycle of the specimens used in culture experiments

Summary

Introduction

Bio-Resources Business Development Division, Riken Food Co., Ltd., Miyagi 985-0844, Japan; Nishina Center for Accelerator-Based Science, RIKEN, Saitama 351-0198, Japan. In addition to the sexual life cycle, several Ulva species, including U. prolifera, are known to have two types of obligate asexual life cycles without sexual reproduction via meiosis and conjugation, reproducing through biflagellate or quadriflagellate diploid zoids specialized for asexual development, these zoids have negative phototaxis [3]. These asexual zoids were termed “zoosporoids” [4,5]. A recent study conducting genome and transcriptome analyses of U. prolifera suggests that the asexual thalli originally evolved via apomeiosis in sporophytic thalli [8]

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Results

Conclusion