Effects of auxin derivatives on phenotypic plasticity and stress tolerance in five species of the green algaDesmodesmus(Chlorophyceae, Chlorophyta)

Abstract

Green microalgae of the genus Desmodesmus are characterized by a high degree of phenotypic plasticity (i.e. colony morphology), allowing them to be truly cosmopolitan and withstand environmental fluctuations. This flexibility enables Desmodesmus to produce a phenotype–environment match across a range of environments broader compared to algae with more fixed phenotypes. Indoles and their derivatives are a well-known crucial class of heterocyclic compounds and are widespread in different species of plants, animals, and microorganisms. Indole-3-acetic acid (IAA) is the most common, naturally occurring plant hormone of the auxin class. IAA may behave as a signaling molecule in microorganisms, and the physiological cues of IAA may also trigger phenotypic plasticity responses in Desmodesmus. In this study, we demonstrated that the changes in colonial morphs (cells per coenobium) of five species of the green alga Desmodesmus were specific to IAA but not to the chemically more stable synthetic auxins, naphthalene-1-acetic acid and 2,4-dichlorophenoxyacetic acid. Moreover, inhibitors of auxin biosynthesis and polar auxin transport inhibited cell division. Notably, different algal species (even different intraspecific strains) exhibited phenotypic plasticity different to that correlated to IAA. Thus, the plasticity involving individual-level heterogeneity in morphological characteristics may be crucial for microalgae to adapt to changing or novel conditions, and IAA treatment potentially increases the tolerance of Desmodesmus algae to several stress conditions. In summary, our results provide circumstantial evidence for the hypothesized role of IAA as a diffusible signal in the communication between the microalga and microorganisms. This information is crucial for elucidation of the role of plant hormones in plankton ecology.

Insights into the Light Response of Skeletonema marinoi: Involvement of Ovothiol

“…These results highlight the phenotypic plasticity of S. marinoi when submitted to different light conditions, with ovothiol involvement into the photoresponse when cells cope with natural high light condition (sinusoidal), while it does not take part to the response of cells to unnatural high light condition. This is a quite interesting issue being that phenotypic plasticity, defined as the ability of an organism's genotype to display different phenotypes in response to the environmental variability, is a key process explaining microalgal adaptability to natural conditions [57][58][59]. In particular, microalgae are adapted to a natural light sinusoidal distribution during the day, allowing them to efficiently cope with light variations, e.g., high light environment, through the activation of different kinds of complementary photoresponses, from the fast non-photochemical quenching or xanthophyll cycle operation to changes in carotenoids levels or in antioxidant network activation.…”

Exogenous Indole-3-Acetic Acid Induced Ethanol Tolerance in Phylogenetically Diverse Saccharomycetales Yeasts

“…The duration of the IAA pretreatment may also be a factor. The durations of IAA pretreatments used in previous studies varied by organism, with durations of 2 h for prokaryotic bacteria ( Bianco et al , 2006 ), 3 h for rhizobia ( Donati et al , 2013 ), 24 h for algae ( Lin et al , 2020 ), and 12 h for yeast ( Sun et al , 2014 ). The durations of the IAA pretreatment used in the present study (24 and 48 h) were sufficient to trigger ethanol tolerance; however, further studies are needed to clarify how the duration of the pretreatment may affect this response.…”

“…and promoted the accumulation of lipid droplets in algal cells, an effect that is related to stress tolerance ( Chung et al , 2018 ). Follow-up studies confirmed that stress tolerance was enhanced in green algae treated with IAA ( Lin et al , 2020 ). Similar mechanisms have been detected in bacteria.…”

“…An increased environmental IAA concentration indicates the aggregation of microorganisms and greater competition ( Geldner et al , 2003 ; Prusty et al , 2004 ; Bianco et al , 2006 ; Teale et al , 2006 ; Reineke et al , 2008 ; Contreras-Cornejo et al , 2009 ; Imperlini et al , 2009 ; Spaepen and Vanderleyden, 2011 ; Donati et al , 2013 ; Kulkarni et al , 2013 ; Sun et al , 2014 ; Fu et al , 2015 ; Liu et al , 2016 ; Chung et al , 2018 ; Lin et al , 2020 ). Under favorable growth conditions, the addition of exogenous IAA was shown to reduce the growth rate of S. cerevisiae ( Prusty et al , 2004 ; Liu et al , 2016 ), but also increased it in the presence of relatively low concentrations of Aureobasidium pullulans (625‍ ‍μM), Cryptococcus flavus (312.5‍ ‍μM), and Fusarium delphinoides (<50‍ ‍μM) ( Kulkarni et al , 2013 ; Sun et al , 2014 ).…”

Sulfur-Containing Marine Bioactives

“…Furthermore, these variations will also depend on the species and its adjustment mechanisms to osmotic stress. For example, in the case of Botryococcus braunii, the increase in salinity allowed a greater production of polysaccharides [59]. Therefore, the increase in EPS production in T. suecica will depend on the cultivation condition, abiotic factors such as salinity and optimization of EPS extraction methods.…”