AtHESPERIN: a novel regulator of circadian rhythms with poly(A)-degrading activity in plants

We report the identification and characterization of a novel gene, <i>AtHesperin</i> (<i>AtHESP</i>) that codes for a deadenylase in <i>Arabidopsis thaliana</i>. The gene is under circadian clock-gene regulation and has similarity to the mammalian <i>Nocturnin</i>. AtHESP can efficiently degrade poly(A) substrates exhibiting allosteric kinetics. Size exclusion chromatography and native electrophoresis coupled with kinetic analysis support that the native enzyme is oligomeric with at least 3 binding sites. Knockdown and overexpression of <i>AtHESP</i> in plant lines affects the expression and rhythmicity of the clock core oscillator genes <i>TOC1</i> and <i>CCA1</i>. This study demonstrates an evolutionary conserved poly(A)-degrading activity in plants and suggests deadenylation as a mechanism involved in the regulation of the circadian clock. A role of <i>AtHESP</i> in stress response in plants is also depicted.