Four SQUAMOSA PROMOTER BINDING PROTEIN-LIKE homologs from a basal eudicot tree (Platanus acerifolia) show diverse expression pattern and ability of inducing early flowering in Arabidopsis

Abstract

Four SPL3/4/5 orthologous genes from Platanus acerifolia were identified, and their structure, expression patterns, role in controlling phase change and ability of inducing early flowering in Arabidopsis were analyzed. Plant flowering behavior is controlled by multiple pathways. The Arabidopsis thaliana SQUAMOSA PROMOTER BINDING PROTEIN-LIKE3/4/5 (AtSPL3/4/5) genes are involved in regulating vegetative phase change. Recent studies have shown that AtSPL3/4/5 genes are directly involved in inducing expression of three flowering integrator genes namely, LEAFY (LFY), FRUITFULL (FUL) and APETALA1 (AP1), thereby triggering flowering. This regulatory integration reveals a commonality of the flowering response with various other plant developmental pathways. We have isolated four SPL3/4/5 orthologous genes (PaSPL3a/b/c/d) from a basal eudicot London plane tree (Platanus acerifolia Wild), a woody species with a long juvenile phase. We investigated the role of these Platanus genes in flowering and detected expression levels between trees in vegetative and reproductive phase. Real-time PCR analysis demonstrated diverse expression patterns for the four PaSPL3 genes throughout the various P. acerifolia tissues, but all four were highly expressed in developing flower bud tissues. Expression of PaSPL3a/b/c in leaves changed according to the season and was regulated by temperature. Furthermore, three of the orthologous were found to induce an early flowering phenotype when overexpressed in Arabidopsis. The findings of this study indicate that PaSPL3 genes may participate in early stage inflorescence development in London Plane. However, there appears to be some divergence in the function of these genes in the control of phase change in London plane as compared to that within Arabidopsis.