Ectopic Expression of a Fagopyrum esculentum APETALA1 Ortholog only Rescues Sepal Development in Arabidopsis ap1 Mutant

Abstract

<i>Fagopyrum esculentum</i> (Polygonaceae: Caryophyllales) exhibits an undifferentiated perianth comprising five showy tepals, which does not completely correspond to the perianth differentiated into typical sepals and petals in most core eudicots. In <i>Arabidopsis</i>, the <i>APETALA1</i> (<i>AP1</i>) gene is involved in specifying sepals and petals development. Here we isolated <i>AP1</i> ortholog, <i>FaesAP1</i>, and a 2.2kb <i>FaesAP1</i> promoter (<i>pFaesAP1</i>) from <i>F. esculentum</i>. <i>FaesAP1</i> expression is mainly detectable in all floral organs and maintains at a high level when tepals elongate rapidly both in pin and thrum flowers. Moreover, the <i>GUS</i> reporter gene driven by <i>pFaesAP1</i> was activated in flowers where the sepals were intense, but the petals very weak or absent. Additionally, <i>FaesAP1</i> ectopic expression in <i>Arabidopsis ap1-10</i> mutant rescues sepal development fully, obviously prompting early flowering, but failing to complement petal development. In this study, evidence was provided that the showy tepals in the <i>F. esculentum</i> are homologs to core eudicots sepals. Furthermore, these findings show a different perianth identity program in Caryophyllales, suggesting that <i>AP1</i> orthologs involved in petal development may evolve independently across different clades of core eudicots. Our results also suggest that <i>FaesAP1</i> holds potential for biotechnical engineering to develop early flowering varieties of <i>F. esculentum.</i>