Divergent functions of two clades of flavodoxin in diatoms mitigate oxidative stress and iron limitation

Abstract

Phytoplankton rely on diverse mechanisms to adapt to the decreased iron bioavailability and oxidative stress-inducing conditions of today’s oxygenated oceans, including replacement of the iron-requiring ferredoxin electron shuttle protein with a less-efficient iron-free flavodoxin under iron limiting conditions. And yet, diatoms transcribe flavodoxins in high-iron regions in contrast to other phytoplankton. Here, we show that the two clades of flavodoxins present within diatoms exhibit a functional divergence, with only clade II flavodoxins displaying the canonical role in adaptation to iron limitation. We created CRISPR/Cas9 knock-outs of the clade I flavodoxin from the model diatomThalassiosira pseudonanaand found these cell lines are hypersensitive to oxidative stress, while maintaining a wild-type response to iron limitation. Within natural diatom communities, clade I flavodoxin transcript abundance is regulated over the diel cycle rather than in response to iron availability, whereas clade II transcript abundances increase either in iron-limiting regions or under artificially induced iron-limitation. The observed functional specialization of two flavodoxin variants within diatoms reiterates two major stressors associated with contemporary oceans and illustrates diatom strategies to flourish in diverse aquatic ecosystems.

Subcellular proteomics for determining iron‐limited remodeling of plastids in the model diatom Thalassiosira pseudonana (Bacillariophyta)

“…In addition to aiding in the elucidation of the diatom plastid-localized proteome, this study compared plastid-enriched proteomes collected from T. pseudonana cultures grown in both Fe-replete and Fe-limiting conditions to identify how the plastid proteome remodels under Fe-limitation. While previous analyses have shown that T. pseudonana has a limited inventory of canonical Fe-sensitive genes, including the lack of an Fe-sensitive isoform of flavodoxin (Graff van Creveld et al, 2023;Morrissey et al, 2015;Whitney et al, 2011), it was chosen for this study as it has a well-characterized Fe-limited transcriptome and whole-cell proteome (Mock et al, 2008;Nunn et al, 2013), a fully sequenced genome (Armbrust et al, 2004), and a plastid-targeted proteome containing 217 proteins (Schober et al, 2019). Within this study, we report the identification of 929 proteins within the plastid-enriched proteome of T. pseudonana across both Fe-limiting and Fe-replete conditions, expanding the inventory of proteins localized within the T. pseudonana plastid proteome.…”