miR398 targets a Cu²⁺-containing Selenium Binding Protein (SBP) in rice and the phylogenetic analysis of the...

MicroRNA 398 (miR398), one of the conserved miRNAs, is known to target multiple genes encoding Cu²⁺-containing proteins such as the conserved two Cu/Zn Superoxide dismutases (CSD1 and CSD2) and a Cu²⁺-chaperone for CSDs (CCS) as primary targets. Additionally, miR398 is known to target transcripts of Cu²⁺-containing proteins such as cytochrome C-oxidase, Cupredoxin, and blue copper binding protein (BCBP) that are poorly conserved among plants.

Our recently generated rice degradomes have validated Selenium Binding Protein (SBP), yet another Cu²⁺-containing protein, as a genuine target of miR398. Because SBP was largely underappreciated target of miR398, we sought to uncover potential conservation of miR398-SBP regulatory module in plants. This analysis revealed that miR398 is targeting SBP transcripts in several monocot clades. Though this regulation was also obvious but less prominent in dicots. Publicly available degradome analysis provided evidence for miR398-induced cleavage on SBP mRNAs in six monocots and four dicots.

These findings suggest that miR398 has picked up SBP as a secondary target in several clades of monocots, but less frequently in dicots. At the biochemical level, SBP proteins, like CSDs, are Cu²⁺-containing proteins that are thought to function in oxidative stress responses. Thus, miR398 regulates diverse families of Cu²⁺-containing proteins (CSDs and SBPs) that are part of the same biochemical pathway.