Life cycle and reproduction dynamics of Bangiales in response to environmental stresses

H2O2 drives the transition from conchocelis to conchosporangia in the red alga Pyropia haitanensis with promotion facilitated by 1-Aminocyclopropane-1-carboxylic acid

The Bangiales represent an ancient lineage within red algae that are characterized by a life history featuring a special transitional stage from diploid to haploid known as the conchosporangia stage. However, the regulatory mechanisms governing the initiation of this stage by changes in environmental conditions are not well understood. This study analyzed the changes in phytohormones and H2O2 content during the development of conchosporangia. It also compared the gene expression changes in the early development of conchosporangia through transcriptome analysis. The findings revealed that H2O2 was shown to be the key signal initiating the transition from conchocelis to conchosporangia in Pyropia haitanensis. Phytohormone analysis showed a significant increase in 1-aminocylopropane-1-carboxylic acid (ACC) levels during conchosporangia maturation, while changes in environmental conditions were found to promote the rapid release of H2O2. H2O2 induction led to conchosporangia development, and ACC enhanced both H2O2 production and conchosporangia development. This promotive effect was inhibited by the NADPH oxidase inhibitor diphenylene iodonium and the H2O2 scavenger N, N'-dimethylthiourea. The balance of oxidative-antioxidative mechanisms was maintained by regulating the activities and transcriptional levels of enzymes involved in H2O2 production and scavenging. Transcriptome analysis in conjunction with evaluation of enzyme and transcription level changes revealed upregulation of protein and sugar synthesis along with modulation of energy supply under the conditions that induced maturation, and exogenous ACC was found to enhance the entire process. Overall, this study demonstrates that ACC enhances H2O2 promotion of the life cycle switch responsible for the transition from a vegetative conchocelis to a meiosis-preceding conchosporangia stage in Bangiales species.

Heat stress memory differentially regulates the expression of nitrogen transporter genes in the filamentous red alga 'Bangia' sp. ESS1

Introduction

To withstand high temperatures that would be lethal to a plant in the naïve state, land plants must establish heat stress memory. The acquisition of heat stress tolerance via heat stress memory in algae has only been observed in the red alga 'Bangia' sp. ESS1.

Methods

In this study, we further evaluated the intrinsic ability of this alga to establish heat stress memory by monitoring hydrogen peroxide (H2O2) production and examining the relationship between heat stress memory and the expression of genes encoding nitrogen transporters, since heat stress generally reduces nitrogen absorption. Next, genes encoding nitrogen transporters were selected from our unpublished transcriptome data of 'Bangia' sp. ESS1.

Results

We observed a reduction in H2O2 content when heat stress memory was established in the alga. In addition, six ammonium transporter genes, a single-copy nitrate transporter gene and two urea transporter genes were identified. Two of these nitrogen transporter genes were induced by heat stress but not by heat stress memory, two genes showed heat stress memory-dependent expression, and one gene was induced by both treatments. Heat stress memory therefore differentially regulated the expression of the nitrogen transporter genes by reducing heat stress-inducible gene expression and inducing heat stress memory-dependent gene expression.

Discussion

These findings point to the functional diversity of nitrogen transporter genes, which play different roles under various heat stress conditions. The characteristic effects of heat stress memory on the expression of individual nitrogen transporter genes might represent an indispensable strategy for reducing the threshold of sensitivity to recurrent high-temperature conditions and for maintaining nitrogen absorption under such conditions in 'Bangia' sp. ESS1.

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

The red alga Neopyropia yezoensis undergoes polarized elongation and asymmetrical cell division of the apical stem cell during tip growth in filamentous generations of its life cycle: the conchocelis and conchosporangium. Side branches are also produced via tip growth, a process involving the regeneration and asymmetrical division of the apical stem cell. Here, we demonstrate that auxin plays a crucial role in these processes by using the auxin antagonist 2-(1H-Indol-3-yl)-4-oxo-4-phenyl-butyric acid (PEO-IAA), which specifically blocks the activity of the auxin receptor TRANSPORT INHIBITOR RESPONSE1 (TIR1) in land plants. PEO-IAA repressed both the regeneration and polarized tip growth of the apical stem cell in single-celled conchocelis; this phenomenon was reversed by treatment with the auxin indole-3-acetic acid (IAA). In addition, tip growth of the conchosporangium was accelerated by IAA treatment but repressed by PEO-IAA treatment. These findings indicate that auxin regulates polarized tip cell growth and that an auxin receptor-like protein is present in N. yezoensis. The sensitivity to different 5-alkoxy-IAA analogs differs considerably between N. yezoensis and Arabidopsis thaliana. N. yezoensis lacks a gene encoding TIR1, indicating that its auxin receptor-like protein differs from the auxin receptor of terrestrial plants. These findings shed light on auxin-induced mechanisms and the regulation of tip growth in plants.