Getting a grip on genetic modification in brown algae.

Brown algae (Phaeophyceae) are remarkable organisms that, independently of parallel developments in green algae and in land plants, evolved multicellularity and organs that look like their “counterparts” in land plants and are accordingly termed rhizoids (resembling root), cauloids (resembling stem), and phylloids (resembling leaf). Similar to trees on land, large brown algae (kelp) can form large underwater forests. While some brown algae show a remarkable difference between size and appearance of gametophytes and sporophytes, these generations of the brown algal life cycle can only be distinguished on the microscopic level in other brown algae (like the homothallic Ectocarpus). The genetic processes steering these complex developmental patterns are still largely unknown. The development and origin of specific structures of brown algal organs began to attract the attention of biologists in the early 1900s. For instance in 1904, when studying archegonia in different phyla, Davis investigated and compared the sporangia and gametangia in Phaeophyceae like Ectocarpus and Dictyota (Davis 1903). Since then, the scientific interest in brown algae increased at the taxonomic level, but also with respect to the characterization of the life cycle (M€ uller 1964), the discovery of pheromones (M€ uller et al. 1979) and various cellular processes including the polarization of Fucus zygotes (Brownlee and Wood 1986). As macroalgae are also considered a potential source of food, gelling agents, biofuels and new bioactive compounds, research on these algae has escalated in recent years. It is unfortunate that for this scientifically and economically interesting group of organisms, a useful set of critical genetic tools, including ways to suppress the activity of specific genes and express heterologous genes, has not been established. To my knowledge, there is only a single report on transient expression of a reporter gene in Laminaria gametophytes (Qin et al. 1994), but for unknown reasons this technique has not been widely used by the research community. Of course there are limitations regarding the use of genetically modified brown algae, and common sense dictates that they should not be released into the oceans. However, the ability to perform genetic manipulations of model brown algal systems under controlled laboratory conditions could strongly increase our understanding of cellular and developmental processes in multicellular algae. Genetic manipulation of other multicellular photoautotrophic organisms like mosses (Physcomitrella patens; Schaefer et al. 1991), land plants (Arabidopsis thali ana; Bent 2000), and green algae (Volvox sp.; Schiedlmeier et al. 1994) are much more advanced. The recent publication of the genome sequence of the brown alga Ectocarpus siliculosus by Cock et al. (2010) has raised expectations that genetic manipulation in brown algae might be feasible sooner or later. However, although different research groups around the globe have tried, a method for the stable genetic transformation of brown algae has yet to be developed. In this issue of the Journal of Phycology, Brownlee et al. report on the first approach to silence genes in the brown alga Fucus serratus (Farnham et al. 2013). As a proof of concept, they decided to study cytoskeleton formation in Fucus zygotes (Fig. 1) as a phenotypic readout of altered gene expression. This was a splendid focus for ‘knockdown’ experiments since the altered cytoskeletal features in the suppressed strains can be readily observed using fluorescence microscopy (Corellou et al. 2005). The authors microinjected double-stranded RNA to induce the degradation of endogenous mRNAs (see Fig. 2), which resulted in reduced expression of the encoded proteins and an observable phenotype. More specifically, they injected fragments of double stranded RNA complementary to genes encoding a-tubulin and b-actin. Similar to earlier pharmacological experiments in which microtubule development was disrupted in Fucus, the authors observed growth arrest and disruption of cell division. The efficacy of the gene silencing approach is suggested by the findings that all zygotes that had been injected with the b-actin fragment failed to develop properly, while 80% of the zygotes injected with control DNA showed a normal developmental progression. The classical way to achieve down-regulation of a gene is by inducing mutations that modify or