Abstract
Diatoms are unicellular phytoplankton accounting for ∼40% of global marine primary productivity
[1], yet the molecular mechanisms underlying their ecological success are largely unexplored. We use a functional-genomics approach in the marine diatom
Phaeodactylum tricornutum to characterize a novel protein belonging to the widely conserved YqeH subfamily
[2] of GTP-binding proteins thought to play a role in ribosome biogenesis
[3], sporulation
[4], and nitric oxide (NO) generation
[5]. Transgenic diatoms overexpressing this gene, designated
PtNOA, displayed higher NO production, reduced growth, impaired photosynthetic efficiency, and a reduced ability to adhere to surfaces. A fused YFP-PtNOA protein was plastid localized, distinguishing it from a mitochondria-localized plant ortholog.
PtNOA was upregulated in response to the diatom-derived unsaturated aldehyde 2E,4E/Z-decadienal (DD), a molecule previously shown to regulate intercellular signaling, stress surveillance
[6], and defense against grazers
[7]. Overexpressing cell lines were hypersensitive to sublethal levels of this aldehyde, manifested by altered expression of superoxide dismutase and metacaspases, key components of stress and death pathways
[8, 9]. NOA-like sequences were found in diverse oceanic regions, suggesting that a novel NO-based system operates in diatoms and may be widespread in phytoplankton, providing a biological context for NO in the upper ocean
[10].