Abstract
ABSTRACTDNA topoisomerase I alpha (TOP1α) plays a specific role in Arabidopsis thaliana development and is required for stem cell regulation in shoot and floral meristems. Recently, a new role independent of meristem functioning has been described for TOP1α, namely flowering time regulation. The same feature had been detected by us earlier for fas5, a mutant allele of TOP1α. In this study we clarify the effects of fas5 on bolting initiation and analyze the molecular basis of its role on flowering time regulation. We show that fas5 mutation leads to a constitutive shade avoidance syndrome, accompanied by leaf hyponasty, petiole elongation, lighter leaf color and early bolting. Other alleles of TOP1α demonstrate the same shade avoidance response. RNA sequencing confirmed the activation of shade avoidance gene pathways in fas5 mutant plants. It also revealed the repression of many genes controlling floral meristem identity and organ morphogenesis. Our research further expands the knowledge of TOP1α function in plant development and reveals that besides stem cell maintenance TOP1α plays an important new role in regulating the adaptive plant response to light stimulus and flower development.
Highlights
DNA topoisomerases function to relieve torsional stress in the DNA helix by introducing transient breaks into the DNA molecule
DNA topoisomerase TOP1α plays a specific role in Arabidopsis thaliana development and is required for stem cell regulation in shoot and floral meristems
A new role independent of meristem functioning has been described for TOP1α, namely, flowering time regulation
Summary
DNA topoisomerases function to relieve torsional stress in the DNA helix by introducing transient breaks into the DNA molecule. These enzymes regulate genome stability and processes of DNA recombination, repair, replication and transcription. Overrepresentation of PcG targets among genes whose expression is altered in the top1α-2 mutant suggests that TOP1α affects PcGmediated epigenetic regulation in Arabidopsis plants (Liu et al, 2014). These findings explain the specific developmental function of TOP1α, which has been actively studied
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