The baseless mutant links protein phosphatase 2A with basal cell identity in the brown alga Ectocarpus

Insights into the molecular bases of multicellular development from brown algae

The transition from simple to complex multicellularity represents a major evolutionary step that occurred in only a few eukaryotic lineages. Comparative analyses of these lineages provide insights into the molecular and cellular mechanisms driving this transition, but limited understanding of the biology of some complex multicellular lineages, such as brown algae, has hampered progress. This Review explores how recent advances in genetic and genomic technologies now allow detailed investigations into the molecular bases of brown algae development. We highlight how forward genetic techniques have identified mutants that enhance our understanding of pattern formation and sexual differentiation in these organisms. Additionally, the existence and nature of morphogens in brown algae and the potential influence of the microbiome in key developmental processes are examined. Outstanding questions, such as the identity of master regulators, the definition and characterization of cell types, and the molecular bases of developmental plasticity are discussed, with insights into how recent technical advances could provide answers. Overall, this Review highlights how brown algae are emerging as alternative model organisms, contributing to our understanding of the evolution of multicellular life and the diversity of body plans.

Repeated co-option of HMG-box genes for sex determination in brown algae and animals

In many eukaryotes, genetic sex determination is not governed by XX/XY or ZW/ZZ systems but by a specialized region on the poorly studied U (female) or V (male) sex chromosomes. Previous studies have hinted at the existence of a dominant male-sex factor on the V chromosome in brown algae, a group of multicellular eukaryotes distantly related to animals and plants. The nature of this factor has remained elusive. Here, we demonstrate that an HMG-box gene acts as the male-determining factor in brown algae, mirroring the role HMG-box genes play in sex determination in animals. Over a billion-year evolutionary timeline, these lineages have independently co-opted the HMG box for male determination, representing a paradigm for evolution's ability to recurrently use the same genetic "toolkit" to accomplish similar tasks.

Red macroalgae in the genomic era

Rhodophyta (or red algae) are a diverse and species-rich group that forms one of three major lineages in the Archaeplastida, a eukaryotic supergroup whose plastids arose from a single primary endosymbiosis. Red algae are united by several features, such as relatively small intron-poor genomes and a lack of cytoskeletal structures associated with motility like flagella and centrioles, as well as a highly efficient photosynthetic capacity. Multicellular red algae (or macroalgae) are one of the earliest diverging eukaryotic lineages to have evolved complex multicellularity, yet despite their ecological, evolutionary, and commercial importance, they have remained a largely understudied group of organisms. Considering the increasing availability of red algal genome sequences, we present a broad overview of fundamental aspects of red macroalgal biology and posit on how this is expected to accelerate research in many domains of red algal biology in the coming years.