Heterologous expression of ELF4 from Chlamydomonas reinhardtii and Physcomitrella patens delays flowering in Arabidopsis thaliana

The circadian clock perceives seasonal changes in day length and temperature and then regulates numerous internal cellular processes. Arabidopsis thaliana EARLY FLOWERING4 (ELF4) is a key circadian clock component that is involved in transcriptional regulation of the central oscillator and multiple output pathways. However, the functions of ELF4 orthologues in other organisms are poorly understood. Here, we identified ELF4 orthologous genes in two non-flowering organisms, the unicellular green alga Chlamydomonas (CrELF4) and the moss Physcomitrella patens (PpELF4). Constitutive expression of CrELF4 and PpELF4 in the Arabidopsis elf4 mutant not only completely rescued its early flowering phenotype, but also induced late flowering. This was associated with decreased transcript levels of CONSTANS (CO) and FLOWERING LOCUS T (FT), two key positive regulators of flowering-time pathways. In addition, expression of CrELF4 and PpELF4 in the Arabidopsis elf4 mutant inhibited hypocotyl elongation and altered the expression of circadian clock-related genes. Taken together, these data suggest that ELF4 orthologous genes in Chlamydomonas and Physcomitrella share an evolutionary conserved role with Arabidopsis ELF4 and indicate that the plant clock component ELF4 is functionally conserved from basal plants to angiosperms.