Ancestral duplicated DL/CRC orthologs display function on orchid reproductive organ innovation

The orchid flower is renowned for complexity of flower organ morphogenesis and has attracted great interest from scientists. The YABBY genes encode plant-specific transcription factors with important roles in vegetative and reproductive development in seed plants.DROOPING LEAF/CRABS CLAW(DL/CRC) orthologs are involved in reproductive organ development (especially carpels) of angiosperms. Orchid gynostemium (the fused organ of the androecium and gynoecium) and ovule development are unique developmental processes. Understanding theDL/CRC-likegenes controlling the developmental program of the gynostemium and ovule could provide accessible information for reproductive organ molecular regulation in orchids. TwoDL/CRC-likegenes, namedPeDL1andPeDL2, were cloned fromPhalaenopsis equestris. The orchid DL/CRC forms a monophyletic clade with two subclades including AshDL, PeDL1 and DcaDL1 in subclade I, and PeDL2 and DcaDL2 in subclade II. The temporal and spatial expression analysis indicatedPeDLgenes are specifically expressed in the gynostemium and at the early stages of ovule development. BothPeDLscould partially complement anArabidopsis crc-1mutant. Transient overexpression ofPeDL1inPhalaenopsisorchids caused abnormal development of ovule and stigmatic cavity of gynostemium. PeDL1, instead of PeDL2, could form a heterodimer with PeCIN8. Paralogue retention and subsequent divergence of the gene sequence ofPeDL1andPeDL2inP. equestrismight result in the differentiation of function and protein behaviors. These results reveal the important roles ofPeDLsinvolved in orchid gynostemium and ovule development and provide new insights for further understanding the molecular mechanisms underlying orchid reproductive organ development.