Sensing Your Surroundings: How Tiny Algae Respond to Environmental Cues

Resident populations of marine algae go through dynamic transformations which are clearly structured by environmental factors – but the responsible factors, or suites of factors, remain mysterious. Macronutrients such as nitrogen can be influential but do not adequately explain temporal and spatial patterns in nature. Because we do not have the depth of biological understanding needed, these organisms elude predictive modeling even though they collectively perform 50% of global CO₂ uptake. One way to gain insight into important chemical, physical and biotic factors behind growth and demise of populations is through exploring their genomes and transcriptional responses, searching for clues, and new hypotheses on important controls – even controlling factors that we may not be able to measure in nature or are unaware of. Large scale sequence surveys are powerful, but the most transformative studies take advantage of this type of data in the context of downstream testing in model taxa and iteration with field studies. Here we will discuss how our view of vitamin control of algal blooms has been revolutionized by the combination of: (i) pathway gap analysis (itself transformed by availability of genome-level sequence data from many taxa), (ii) the discovery of widespread chemical-sensing molecular switches harbored by algae, and (iii) hypothesis testing in relevant marine taxa. We will then turn to a specific group of algae that are sister to land plants. Photosynthesis on land is performed by organisms that arose from the primary endosymbiosis event, whereby a eukaryotic cell engulfed a cyanobacterium that then became the organelle where photosynthesis occurs. Prasinophytes are unicellular algae that form a sister group to plants alongside distantly related model green algae like Chlamydomonas. Prasinophytes possess characteristics thought to reflect components of the ancestral alga that gave rise to plants and are important in marine environments from the tropics to poles. Massive transcriptome sequencing is leading to new discoveries on the environmental sensing abilities of these algae. These research innovations are not only helping scientists to understand how phytoplankton navigate dynamic marine systems but are also providing insights into plant evolution and the origins of specific plant machineries. Collectively, such studies are fundamentally changing our knowledge of photosynthetic processes, microbial interactions and marine ecology.