The pea photoperiod response locus STERILE NODES is an ortholog of LUX ARRHYTHMO

The STERILE NODES (SN) locus in pea (Pisum sativum L.) was one of the first photoperiod-response genes to be described, and provided early evidence for the genetic control of long-distance signaling in flowering-time regulation. Lines homozygous for recessive sn mutations are early-flowering and photoperiod insensitive, with an increased ability to promote flowering across a graft union in short-day conditions. Here we show that SN controls developmental regulation of genes in the FT family and rhythmic regulation of genes related to circadian clock function. Using a positional and functional candidate approach we identify SN as the pea ortholog of Arabidopsis LUX ARRHYTHMO (LUX), a GARP transcription factor with an important role in circadian clock function. In addition to induced mutants, sequence analysis demonstrates the presence of at least three other independent, naturally-occurring loss-of-function mutations among known sn cultivars. Examination of genetic and regulatory interactions between SN and two other circadian clock genes HIGH RESPONSE TO PHOTOPERIOD (HR) and DIE NEUTRALIS (DNE) suggests a complex relationship in which HR regulates expression of SN and the role of DNE and HR in control of flowering is dependent on SN. These results extend previous work to show that pea orthologs of all three Arabidopsis "evening complex" genes regulate clock function and photoperiod-responsive flowering, and suggest that the function of these genes may be widely conserved.