Biology subjects

Suetsugu, K.

Publications and source records attributed to Suetsugu, K..

4 recordsLinked to original sources

bioRxiv2024

Responses of chlorophyll fluorescence to CO2 elimination as an indicator of Crassulacean acid metabolism photosynthesis

Crassulacean acid metabolism (CAM) is found in a wide variety of vascular plant species, mainly those inhabiting water-limited environments. Identifying and characterizing diverse CAM species enhances our understanding of the physiological, ecological, and evolutionary significance of CAM photosynthesis. In this study, we examined the effect of CO2 elimination on chlorophyll fluorescence-based photosynthetic parameters in two constitutive CAM Kalanchoe species and six orchids. In CAM-performing Kalanchoe species, the effective quantum yield of photosystem II showed no change in response to CO2 elimination during the daytime but decreased with CO2 elimination at dusk. We applied this method to reveal the photosynthetic mode of epiphytic orchids and found that Gastrochilus japonicus, Oberonia japonica, and Bulbophyllum inconspicuum, but not Bulbophyllum drymoglossum, are constitutive CAM. Although B. drymoglossum had relatively high malate content in leaves, they did not depend on it to perform photosynthesis even under water deficient or high light conditions. Anatomical comparisons revealed a notable difference in the leaf structure between B. drymoglossum and B. inconspicuum; B. drymoglossum leaves possess the large water storage tissue internally, unlike B. inconspicuum leaves, which develop pseudobulbs. Our data propose a novel approach to identify and characterize CAM plants without labor-intensive experimental procedures. HighlightResponses of chlorophyll fluorescence-based photosynthetic parameters to CO2 elimination differ between Crassulacean acid metabolism (CAM) and C3 metabolism, proposing a novel approach to identify and characterize CAM plants.

plant biology↗

bioRxiv2023

Fruitless mating with the exes: the irreversible parthenogenesis in a stick insect

Parthenogenetic lineages, common in many animals, have sparked debate about their evolutionary persistence. While asexuality is expected to ensure reproductive assurance and provide a demographic advantage, parthenogens should suffer from the lack of gene shuffling with other individuals. On the other hand, occasional sexual reproduction has been theoretically predicted to be enough to mitigate the long-term costs of parthenogenesis. Recent studies have revealed instances of cryptic sex in some old parthenogenetic lineages, which is most likely mediated by rarely occurring males. Unlike female traits that rapidly become vestigial under asexuality, traits in males have been predicted to slowly decay due to the accumulation of neutral mutations over long evolutionary times. In fact, rare males often retain sexual functions, raising questions about the asexuality of these long-standing parthenogenetic lineages. Here, we intensively examined the possibility of sexual reproduction in the Japanese common stick insect, Ramulus mikado, which was also suggested to be an old parthenogen in our previous work. While asexual female reproduction appears to be quite predominant throughout Japan, we fortunately obtained the rare males from the field. These males exhibited typical stick insect male morphology and engaged in mating behaviors with conspecific females. However, no paternal-specific alleles were detected in the offspring; all embryos showed genotypes identical to their mothers. Our histological observations on a few males revealed that they had no sperm in their reproductive organs, although the degree of decay may be different among the lineages. We also found that females have sexual organs with signs of degeneration. All these results demonstrate the irreversible asexual reproduction of R. mikado and indicate their long history as a parthenogenetic species. Our present study provides unique insights into the maintenance of parthenogenesis and degenerative evolution of sexual traits in ancient asexual lineages.

evolutionary biology↗

bioRxiv2023

Phylogeographical evidence for historical long-distance dispersal in the flightless stick insect Ramulus mikado

Exploring how organisms overcome geographical barriers to dispersal is a fundamental question in biology. Passive long-distance dispersal events, although infrequent and unpredictable, have a considerable impact on species range expansions. Despite limited active dispersal capabilities, many stick insect species have vast geographical ranges, indicating that passive long-distance dispersal is vital for their distribution. A potential mode of passive dispersal in stick insects is via the egg stage within avian digestive tracts, as suggested by experimental evidence. However, detecting such events under natural conditions is challenging due to their rarity. To indirectly assess the importance of historical avian-mediated dispersal, we examined the population genetic structure of the flightless stick insect Ramulus mikado based on a multifaceted molecular approach (COI haplotypes, nuclear SSR markers, and genome-wide SNPs). Subsequently, we identified unique phylogeographic patterns, including the discovery of identical COI genotypes spanning considerable distances, which substantiates the notion of passive long-distance genotypic dispersal. Overall, all the molecular data revealed low and mostly non-significant genetic differentiation among populations, with identical or very similar genotypes across distant populations. We propose that long-distance dispersal facilitated by birds is the most plausible explanation for the unique phylogeographic pattern observed in this flightless stick insect.

evolutionary biology↗

bioRxiv2023

Orchid seed germination through auto-activation of mycorrhizal symbiosis signaling regulated by gibberellin

Orchids parasitically depend on external nutrients from mycorrhizal fungi for seed germination. Previous findings suggest that orchids utilize a genetic system of mutualistic arbuscular mycorrhizal (AM) symbiosis to establish parasitic symbiosis. In AM symbiosis, recent studies have revealed that the plant hormone gibberellin (GA) negatively affects fungal colonization and development. Although previous studies imply that GA is important for orchid mycorrhizal symbiosis, the molecular mechanism of seed germination in which mycorrhizal symbiosis co-occurs remains unclear because, in AM plants, GA regulates seed germination and symbiosis positively and negatively, respectively. To elucidate this conflict, we investigated the effect of GA on Bletilla striata seed germination and mycorrhizal symbiosis using asymbiotic and symbiotic germination methods. Additionally, we compared the transcriptome profiles between asymbiotically and symbiotically germinated seeds. Exogenous GA negatively affected seed germination and fungal colonization, and endogenous bioactive GA was actively converted to the inactive form during seed germination. Transcriptome analysis showed that B. striata shared many of the induced genes between asymbiotically and symbiotically germinated seeds, including GA metabolism- and signaling-related genes and AM-specific marker homologs. Our study suggests that orchids have evolved in a manner that they do not use bioactive GA as a positive regulator of seed germination and instead, auto-activate the mycorrhizal symbiosis pathway through GA inactivation to accept the fungal partner immediately during seed germination.

plant biology↗