AvaKa, a protein of unknown function, contributes to iron homeostasis in the cyanobacterium Anabaena sp. strain PCC 7120

Water is indispensable to life, yet some cyanobacteria inhabit hyper-arid deserts and withstand complete desiccation. However, the molecular mechanisms enabling such acclimation remain incompletely understood. In Anabaena sp. strain PCC 7120, the gene avaKa, which encodes a protein of unknown function, has been shown to be required for desiccation tolerance. Here, we characterized the avaKa disruptant DRavaKa under dehydration-related stress conditions. DRavaKa displayed hypersensitivity to EDTA, and transcripts of iron-deficiency-inducible genes (isiA1, isiB, furA, and sufB) were elevated even in the absence of EDTA. Whole-cell absorption spectra of DRavaKa revealed a blue shift of the chlorophyll absorption peak, a characteristic feature of iron-deficient cyanobacteria. In addition, the oxidative-stress-inducible gene trxA2 was likewise upregulated. These results indicate that AvaKa contributes to iron homeostasis and that iron deficiency-induced oxidative stress likely underlies the dehydration sensitivity of DRavaKa.