Abstract
Double-flower Eriobotrya japonica, of which one phenotype is homeotic transformation of sepals into petals, is a new germplasm for revealing the molecular mechanisms underlying the floral organ transformation. Herein, we analyzed the sequence, expression pattern and functional characterization of EjPI, which encoded a B-class floral homeotic protein referred to as PISTILLATA ortholog, from genetically cognate single-flower and double-flower E. japonica. Phylogenetic analysis suggested that the EjPI gene was assigned to the rosids PI/GLO lineage. Analysis of protein sequence alignments showed that EjPI has typical domains of M, I, K, and C, and includes a distinctive PI motif at the C-terminal region. Compared with asterids PI/GLO lineage, the K1 and K3 subdomains of EjPI both contain a single amino acid difference. Subcellular localization of EjPI was determined to be in the nucleus. Expression pattern analysis revealed that EjPI expressed not only in petals, filament, and anther in single-flower E. japonica, but also in petaloid sepals in double-flower E. japonica. Meanwhile, there were high correlation between EjPI transcript level and petaloid area within a sepal. Furthermore, 35S::EjPI transgenic wild-type Arabidopsis caused the homeotic transformation of the first whorl sepals into petaloid sepals. Ectopic expression of EjPI in transgenic pi-1 mutant Arabidopsis rescued normal petals and stamens. These results suggest expression pattern of EjPI is associated with the formation of petaloid sepal. Our study provides the potential application of EjPI for biotechnical engineering to create petaloid sepals or regulate floral organ identity in angiosperms.
Highlights
Structural diversification of flower organs has often been considered to be function requirements of floral pollination/ ecology biology (Endress, 2006)
Ectopic expression of the EjPI in homozygous pi-1 mutant Arabidopsis rescued normal petals and stamens. These results reveal that expression pattern of EjPI is associated with the formation of petaloid sepal in double-flower E. japonica
Flower buds from the singleflower and double-flower E. japonica were collected from an experimental farm of Southwest University (Chongqing, China)
Summary
Structural diversification of flower organs has often been considered to be function requirements of floral pollination/ ecology biology (Endress, 2006). The MIKC-type MADS-box transcription factors are identified originally as floral homeotic proteins, and exhibit the characteristic domains from N- to C-terminus: a MADS (M), an intervening (I), a keratin-like (K), and a C-terminal (C) domains (Purugganan et al, 1995; Theißen et al, 1996; Theissen et al, 2000; Kaufmann et al, 2005; Litt and Kramer, 2010) Among these domains, the M domain, which is the most highly conserved region, contributes to the dimerization and nuclear localization (Gramzow and Theissen, 2010). Sequence differences of the MADS-box proteins from different flowering plant species has been used to clarify the evolution and diversification of floral organ identity (Theißen et al, 2016)
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