AUTHOR=Ma Jiang , Shen Xiangling , Liu Zhixiong , Zhang Dechun , Liu Wen , Liang Hongwei , Wang Yubing , He Zhengquan , Chen Faju 

TITLE=Isolation and Characterization of AGAMOUS-Like Genes Associated With Double-Flower Morphogenesis in Kerria japonica (Rosaceae)

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00959

DOI=10.3389/fpls.2018.00959

ISSN=1664-462X

ABSTRACT=<p>Double-flower phenotype is more popular and attractive in garden and ornamental plants. There is great interest in exploring the molecular mechanisms underlying the double-flower formation for further breeding and selection. <italic>Kerria japonica</italic>, a commercial ornamental shrub of the Rosaceae family, is considered an excellent system to determine the mechanisms of morphological alterations, because it naturally has a single-flower form and double-flower variant with homeotic conversion of stamens into petals and carpels into leaf-like carpels. In this study, <italic>Sf-KjAG</italic> (<italic><underline>AG</underline>AMOUS</italic> homolog of <underline>s</underline>ingle-<underline>f</underline>lower <italic><underline>K</underline>. <underline>j</underline>aponica</italic>) and <italic>Df-KjAG</italic> (<italic><underline>AG</underline>AMOUS</italic> homolog of <underline>d</underline>ouble-<underline>f</underline>lower <italic><underline>K</underline>. <underline>j</underline>aponica</italic>) were isolated and characterized as two <italic>AGAMOUS</italic> (<italic>AG</italic>) homologs that occur strictly in single- and double-flower <italic>K. japonica</italic>, respectively. Our sequence comparison showed that <italic>Df-KjAG</italic> is derived from ectopic splicing with the insertion of a 2411 bp transposon-like fragment, which might disrupt mRNA accumulation and protein function, into intron 1. Ectopic expression analysis in <italic>Arabidopsis</italic> revealed that <italic>Sf-KjAG</italic> is highly conserved in specifying carpel and stamen identities. However, <italic>Df-KjAG</italic> did not show any putative C-class function in floral development. Moreover, yeast-two-hybrid assays showed that Sf-KjAG can interact with KjAGL2, KjAGL9, and KjAP1, whereas Df-KjAG has lost interactions with these floral identity genes. In addition, loss-of-function of <italic>Df-KjAG</italic> affected not only its own expression, but also that of other putative floral organ identity genes such as <italic>KjAGL2, KjAGL9, KjAP1, KjAP2, KjAP3</italic>, and <italic>KjPI</italic>. In conclusion, our findings suggest that double-flower formation in <italic>K. japonica</italic> can be attributed to <italic>Df-KjAG</italic>, which appears to be a mutant produced by the insertion of a transposon-like fragment in the normal <italic>AG</italic> homolog (<italic>Sf-KjAG</italic>) of single-flower <italic>K. japonica</italic>.</p><p><bold>Highlights:</bold><italic>Sf-KjAG</italic> and <italic>Df-KjAG</italic> are different variations only distinguished by a transposon-like fragment insertion which lead to the evolutionary transformation from single-flower to double-flowers morphogenesis in <italic>Kerria japonica</italic>.</p>