EjTFL1 Genes Promote Growth but Inhibit Flower Bud Differentiation in Loquat

Abstract

<i>TERMINAL FLOWER1</i> (<i>TFL1</i>), a key factor belonging to the phosphatidyl ethanolamine-binding protein (PEBP) family, controls flowering time and inflorescence architecture in some plants. However, the role of <i>TFL1</i> in loquat remains unknown. In this study, we cloned two <i>TFL1</i>-like genes (<i>EjTFL1-1</i> and <i>EjTFL1-2</i>) with conserved deduced amino acid sequences from cultivated loquat (<i>Eriobotrya japonica</i> Lindl.). First, we determined that flower bud differentiation occurs at the end of June and early July, and then comprehensively analyzed the temporal and spatial expression patterns of these <i>EjTFL1s</i> during loquat growth and development. We observed the contrasting expression trends for <i>EjTFL1s</i> and <i>EjAP1s (APETALA 1)</i> in shoot apices, and <i>EjTFL1s</i> were mainly expressed in young tissues. In addition, short-day and exogenous GA₃ treatments promoted the expression of <i>EjTFL1s</i>, and no flower bud differentiation was observed after these treatments in loquat. Moreover, EjTFL1s were localized to the cytoplasm and nucleus, and both interacted with another flowering transcription factor, EjFD, in the nucleus, and EjTFL1s-EjFD complex significantly repressed the promoter activity of <i>EjAP1-1</i>. The two <i>EjTFL1s</i> were overexpressed in wild-type <i>Arabidopsis thaliana</i> Col-0, which delayed flowering time, promoted stem elongation, increased the number of branches, and also affected flower and silique phenotypes. In conclusion, our results suggested that <i>EjTFL1-1</i> and <i>EjTFL1-2</i> do not show the same pattern of expression whereas both are able of inhibiting flower bud differentiation and promoting vegetative growth in loquat by integrating GA₃ and photoperiod signals. These findings provide useful clues for analyzing the flowering regulatory network of loquat and provide meaningful references for flowering regulation research of other woody fruit trees.