Photoperiod (day length) measurement allows organisms to prepare for seasonal biotic and abiotic stresses. The most well-studied photoperiodic process is the seasonal timing of reproduction to provide offspring with the highest chances of survival. For example, the model plant Arabidopsis flowers when the length of the day exceeds the length of the night, but enters a dormancy state when the length of the day is short. However, other photoperiodic pathways are not yet well characterized. By datamining an existing microarray database and analyzing daily gene expression in short day (winter) and long day (summer) photoperiods, we investigate the correlation between photoperiodic gene expression patterns and gene expression levels. We identify a group of genes, which we name winter genes, that have similar expression patterns and are highly induced under short day conditions. We selected a representative winter gene, an F-box type E3 ligase named Phloem Protein 2-A13 (PP2-A13), and developed a unique luciferase reporter using the promoter of PP2-A13 to query the mechanisms of photoperiodic regulation of the winter genes. We find that PP2-A13 exhibits a two-peak expression pattern which is a hallmark of winter gene expression, and determine that energy status and light signaling each regulate one of the two peaks. Moreover, we demonstrate the winter developmental importance of PP2-A13 by demonstrating that mutants of PP2-A13 have decreased fresh weight and early leaf senescence but only under short day photoperiod conditions. Double mutant analyses show that PP2-A13 is required beside the autophagy pathway for normal plant growth and development in winter photoperiod growth conditions, suggesting that they may act in parallel pathways towards winter plant survival. This work uncovers a conserved novel photoperiod dependent transcriptional switch that regulates plant cell death, which could be applied to crops for optimization of seasonal change responses.
Coauthors: Ann Feke – Yale university;Joshua Gendron – Yale university;Ted Leung – Yale University;Daniel Tarte – Yale University