Down regulation ofAPETALA3 homolog resulted in defect of floral structure critical to explosive pollen release inCornus canadensis

Abstract

In mature buds of the dwarf dogwood lineage (DW) of Cornus, petals and filaments form an “x”‐like box containing mechanical energy from the filaments to allow explosive pollen dispersal. As a start to understand the molecular mechanisms responsible for the origin of this unique structure in Cornus, we cloned and characterized the sequences of APETALA3 (AP3) homologs from Cornus canadensis of the DW lineage and five other Cornus species, given the function of AP3 on petal and stamen development in Arabidopsis, and tested the function of CorcanAP3 using a stable Agrobacterium‐mediated transformation system. The cloned CorAP3s (AP3‐like genes in Cornus) were confirmed to belong to the euAP3 lineage. qRT‐PCR analysis indicated strong increase of CorcanAP3 expression in floral buds of wildtype C. canadensis. A hairpin construct of CorcanAP3 was successfully introduced into wild type plants of C. canadensis, resulting in significant reduction of CorcanAP3 expression and abnormal floral development. The abnormal floral buds lost the “x” form and opened immaturely due to delay or retard of petal and stamen elongation and the push of style elongation. The results suggested CorcanAP3 may function to regulate the coordinated rate of development of petals and stamens in C. canadensis, necessary for the x‐structure formation, although the exact molecular mechanism remains unclear. Comparison among six Cornus species indicated a greater ratio of stamen to petal and style growth in C. canadensis, suggesting an evolutionary change of CorAP3 expression pattern in the DW lineage, leading to the greater growth of filaments to form the “x”‐box.

An updated phylogeny, biogeography, and PhyloCode‐based classification of Cornaceae based on three sets of genomic data

“…An updated classification is proposed using the PhyloCode with the hope to stabilize the names of this taxonomically highly controversial group. During the past two decades, the dogwood genus has become a model clade for bridging macro‐ and microevolution (Fan et al, 2004, 2007; Xiang et al, 2005, 2008; Xiang and Thomas, 2008; Zhang et al, 2008; Yu et al, 2017; Dong et al, 2019; Lindelof et al, 2020; Melton et al, 2020), for integrating phylogenetics, evolution, and developmental biology and molecular genetics (Feng et al 2009b, 2011, 2012, 2013; Liu et al, 2013; Zhang et al, 2013; Geng et al, 2016; Liu et al, 2016, 2017, 2019; Ma et al, 2017), and for integrating evolution with genetics, metabolomics, physiology, and/or ecology (Karlson et al, 2004; Sarnighausen et al, 2004; Call et al, 2016; Pais et al, 2017, 2018, 2020; Zhou 2021). Our study is also an important step facilitating further comparative studies, via a robust phylogeny that we provide as a framework for synthesizing different dimensions of dogwood biology that have been studied for many decades (e.g., Bate‐Smith et al, 1975; Eyde, 1988; Murrell, 1993, 1994; Xiang et al, 1993, 1998; Noshiro and Baas, 1998, 2000, and subsequent publications from the Xiang lab).…”

Evolution, development, and genetics of floral display—form, size, and arrangement

“…Despite its importance to angiosperm diversification, our knowledge of the evolutionary patterns and the underlying developmental and genetic basis of the floral display is still limited. In the modern times, with the advent of integrating approaches among phylogenetics, ecology, molecular genetics, and development, plant biologists have begun to shed lights on the evolutionary patterns, the underlying driving forces, and the developmental and molecular basis of the floral diversity in some angiosperm lineages (e.g., Gerrath et al, ; Kulbaba et al, ; Liu et al, ; Nikolov & Davis, ; Schrager‐Lavelle et al, ; Zhang et al, ; see review by Ma et al, , this issue).…”

“…Most works presented at the symposium were included in this special issue of Journal of Systematics and Evolution . This issue includes both reviews and research papers reporting works on diverse angiosperm lineages, from dicots (Gerrath et al, ; Kulbaba et al, ; Liu et al, ; Nikolov & Davis, ; Zhang et al, ) to monocots (Schrager‐Lavelle et al, ), from autotrophs (Gerrath et al, ; Kulbaba et al, ; Liu et al, ; Schrager‐Lavelle et al, ; Zhang et al, ) to heterotrophs (Nikolov & Davis, ), and from ecological (Kulbaba et al, ) to morphological and molecular aspects (Gerrath et al, ; Liu et al, ; Nikolov & Davis, ; Schrager‐Lavelle et al, ; Zhang et al, ).…”

“…Three research articles included in this issue reported the patterns on floral display in Cornaceae, Solanaceae, and Ranunculaceae through molecular genetic, phylogenetic, and ecological studies. Liu et al () explored the function and role of the AP3 gene homolog in the evolution of explosive pollen release in Cornus canadensis (Cornaceae). Using a stable Agrobacterium‐mediated transformation technique and comparative gene expression methods, they found that a proper level of expression of the AP3 gene during floral development plays important roles in the formation of a special floral structure that is essential to the catapult pollen release unique to the herbaceous lineage of Cornus .…”