Identification and characterization of FRUITFULL-like genes from Platanus acerifolia, a basal eudicot tree.

The function of euAP1 and euFUL in AP1/FUL lineage have been well characterized in core eudicots, and they play common and distinct roles in plant development. However, the evolution and function of FUL-like genes is poorly understood in basal eudicots. In this study, we identified three FUL-like genes PlacFL1/2/3 from London plane (Platanus acerifolia). Sequence alignment and phylogenetic analysis indicated that PlacFL1/2/3 are AP1/FUL orthologs and encoded proteins containing FUL motif and paleoAP1 motif. Quantitative real-time PCR (qRT-PCR) analysis showed that PlacFL1/2/3 were expressed in both vegetative and reproductive tissues, but with distinct spatiotemporal patterns. In contrast to PlacFL1 and PlacFL3, PlacFL2 exhibited higher expression levels and broader expression regions, and that the expression of PlacFL2 gene showed a decreasing and increasing tendency in subpetiolar buds during dormancy induction and breaking, respectively. Overexpression of PlacFLs in Arabidopsis and PlacFL3 in tobacco resulted in early flowering, as well as early termination of inflorescence meristems for transgenic Arabidopsis plants. The expression changes of flowering time and flower meristem identity genes in transgenic Arabidopsis lines with different PlacFLs suggested that PlacFL2 and PlacFL3 may regulate different downstream genes to perform divergent functions. Yeast two-hybrid analysis indicated that PlacFLs interacted strongly with PlacSEP proteins, and PlacFL3 instead of PlacFL1 and PlacFL2 could also form a homodimer and interact with D-class proteins. Our results suggest that PlacFLs may play conserved functions in regulating flowering and flower development, and PlacFL2 might also be involved in dormancy regulation. The research helps us to understand the functional evolution of FUL-like genes in basal eudicots, especially in perennial woody species.

Functional conservation and divergence of five SEPALLATA-like genes from a basal eudicot tree, Platanus acerifolia.

MAIN CONCLUSION: Five SEP -like genes were cloned and identified from Platanus acerifolia through the analysis of expression profiles, protein-protein interaction patterns, and transgenic phenotypes, which suggested that they play conservative and diverse functions in floral initiation and development, fruit development, bud growth, and dormancy. SEPALLATA (SEP) genes have been well characterized in core eudicots and some monocots, and they play important and diverse roles in plant development, including flower meristem initiation, floral organ identity, and fruit development and ripening. However, the knowledge on the function and evolution of SEP-like genes in basal eudicot species is very limited. Here, we cloned and identified five SEP-like genes from London plane (Platanus acerifolia), a basal eudicot tree that is widely used for landscaping in cities. Sequence alignment and phylogenetic analysis indicated that three genes (PlacSEP1.1, PlacSEP1.2, and PlacSEP1.3) belong to the SEP1/2/4 clade, while the other two genes (PlacSEP3.1 and PlacSEP3.2) are grouped into the SEP3 clade. Quantitative real-time PCR (qRT-PCR) analysis showed that all PlacSEPs, except PlacSEP1.1 and PlacSEP1.2, were expressed during the male and female inflorescence initiation, and throughout the flower and fruit development process. PlacSEP1.2 gene expression was only detected clearly in female inflorescence at April. PlacSEP1.3 and PlacSEP3.1 were also expressed, although relatively weak, in vegetative buds of adult trees. No evident PlacSEPs transcripts were detected in various organs of juvenile trees. Overexpression of PlacSEPs in Arabidopsis and tobacco plants resulted in different phenotypic alterations. 35S:PlacSEP1.1, 35S:PlacSEP1.3, and 35S:PlacSEP3.2 transgenic Arabidopsis plants showed evident early flowering, with less rosette leaves but more cauline leaves, while 35S:PlacSEP1.2 and PlacSEP3.1 transgenic plants showed no visible phenotypic changes. 35S:PlacSEP1.1 and 35S:PlacSEP3.2 transgenic Arabidopsis plants also produced smaller and curled leaves. Overexpression of PlacSEP1.1 and PlacSEP3.1 in tobacco resulted in the early flowering and producing more lateral branches. Yeast two-hybrid analysis indicated that PlacSEPs proteins can form homo- or hetero-dimers with the Platanus APETALA1 (AP1)/FRUITFULL (FUL), B-, C-, and D-class MADS-box proteins in different interacting patterns and intensities. Our results suggest that the five PlacSEP genes may play important and divergent roles during floral initiation and development, as well as fruit development, by collaborating with FUL, B-, C-, and D-class MADS-box genes in London plane; PlacSEP1.3 and PlacSEP3.1 genes might also involve in vegetative bud growth and dormancy. The results provide valuable data for us to understand the functional evolution of SEP-like genes in basal eudicot species.