IDENTIFICATION AND COMPARATIVE GENOMIC ANALYSIS OF SIGNALING AND REGULATORY COMPONENTS IN THE DIATOM THALASSIOSIRA PSEUDONANA¹

Abstract

Diatoms are unicellular brown algae that likely arose from the endocytobiosis of a red alga into a single‐celled heterotroph and that constitute an algal class of major importance in phytoplankton communities around the globe. The first whole‐genome sequence from a diatom species, Thalassiosira pseudonana Hasle et Heimdal, was recently reported, and features that are central to diatom physiology and ecology, such as silicon and nitrogen metabolism, iron uptake, and carbon concentration mechanisms, were described. Following this initial study, the basic cellular systems controlling cell signaling, gene expression, cytoskeletal structures, and response to stress have been cataloged in an attempt to obtain a global view of the molecular foundations that sustain such an ecologically successful group of organisms. Comparative analysis with several microbial, plant, and metazoan complete genome sequences allowed the identification of putative membrane receptors, signaling proteins, and other components of central interest to diatom ecophysiology and evolution. Thalassiosira pseudonana likely perceives light through a novel phytochrome and several cryptochrome photoreceptors; it may lack the conserved RHO small‐GTPase subfamily of cell‐polarity regulators, despite undergoing polarized cell‐wall synthesis; and it possesses an unusually large number of heat‐shock transcription factors, which may indicate the central importance of transcriptional responses to environmental stress. The availability of the complete gene repertoire will permit a detailed biochemical and genetic analysis of how diatoms prosper in aquatic environments and will contribute to the understanding of eukaryotic evolution.

Predictable and efficient carbon sequestration in the North Pacific Ocean supported by symbiotic nitrogen fixation

“…The phenomenon of photoperiodism is not well-studied in marine phytoplankton, but the presence of phytochromes in nearly all cyanobacteria and eukaryotic algae studied to date, including marine diatoms (68), suggests that these light-activated molecular switches may be common in the sea. Thus, we propose that activation of phytochromes by astronomical influences, especially variations in photoperiod following the "turning of the sun," may initiate a genetically controlled cascade of molecular and metabolic processes that ultimately define the end of summer and trigger the SEP that we describe herein.…”

Genome-wide diel growth state transitions in the diatom Thalassiosira pseudonana

“…The ability of diatoms to adjust their physiology in response to the diurnal cycle and growth phase fundamentally depends on sensing, signaling, and regulatory mechanisms (38,39). The expression levels of 41% of known transcription factors, 35% of all potential signaling domains, and 31% of genes involved in chromatin state dynamics were up-regulated under one or more of the four identified growth states (Fig.…”

“…These include photomorphogenesis and the entrainment of the circadian clock in higher plants (40). Diatoms contain multiple photoreceptors to sense and respond to light signals of varying and specific spectral properties (38,39). In T. pseudonana, one (far) red-light photoreceptor (diatom phytochrome DPh), four blue-light cryptochrome/photolyase family proteins (CPF1-4), and four aureochrome-like blue-light-regulated transcription factors have been identified (38,39,41,42).…”

Modulation of host ROS metabolism is essential for viral infection of a bloom-forming coccolithophore in the ocean

“…Opposing the classical view of phytoplankton cells as only passive drifters, recent research conducted on diverse phytoplankton have shown their ability to sense and respond to changing environmental conditions by employing specific acclimation mechanisms (Falciatore et al, 2000;Vardi et al, 2002Vardi et al, , 2006Montsant et al, 2007;Taylor, 2009;McLachlan et al, 2012;Graff van Creveld et al, 2014).…”