Solanum tuberosum ZPR1 encodes a light-regulated nuclear DNA-binding protein adjusting the circadian expression of StBBX24 to light cycle

ZPR1 proteins belong to the C4-type of zinc finger coordinators known in animal cells to interact with other proteins and participate in cell growth and proliferation. In contrast, the current knowledge regarding plant ZPR1 proteins is very scarce. Here, we identify a novel potato nuclear factor belonging to this family and named StZPR1. StZPR1 is specifically expressed in photosynthetic organs during the light period, and the ZPR1 protein is located in the nuclear chromatin fraction. From modelling and experimental analyses, we reveal the StZPR1 ability to bind the circadian DNA cis motif CAACAGCATC', named CIRC and present in the promoter of the clock-controlled double B-boxStBBX24 gene, the expression of which peaks in the middle of the day. We found that transgenic lines silenced for StZPR1 expression still display a 24h period for the oscillation of StBBX24 expression but delayed by 4h towards the night. Importantly, other BBX genes exhibit altered circadian regulation in these lines. Our data demonstrate that StZPR1 allows fitting of the StBBX24 circadian rhythm to the light period and provide evidence that ZPR1 is a novel clock-associated protein in plants necessary for the accurate rhythmic expression of specific circadian-regulated genes. In this work, we report about the characterization in potato of a novel nuclear chromatin-located factor belonging to the ZPR1 family and named StZPR1. We reveal the StZPR1 ability to bind the circadian DNA cis motif CAACAGCATC', named CIRC and present in the promoter of the clock-controlled StBBX24 gene. We found that the clock-controlled expression pattern of StBBX24 is affected and delayed by 4h towards the night in transgenic lines silenced for StZPR1 expression. Importantly, other BBX genes exhibit altered circadian regulation in these lines. We conclude that ZPR1 is a novel clock-associated protein in plants necessary for the accurate rhythmic expression of specific circadian-regulated genes.