title: Abaxial Greening Phenotype in Hybrid Aspen.
abstract: The typical angiosperm leaf, as in Arabidopsis, is bifacial consisting of top (adaxial) and bottom (abaxial) surfaces readily distinguishable by the underlying cell type (palisade and spongy mesophyll, respectively). Species of the genus Populus have leaves that are either conventionally bifacial or isobilateral. Isobilateral leaves have palisade mesophyll on the top and bottom of the leaf, making the two sides virtually indistinguishable at the macroscopic level. In poplars this has been termed the "abaxial greening" phenotype. Previous work has implicated ASYMMETRIC LEAVES1 (AS1) as an essential determinant of palisade mesophyll development. This gene, as well as other genes (84 in all) putatively involved in setting the dorsiventral axis of leaves, were investigated in two Populus species: black cottonwood (Populus trichocarpa) and hybrid aspen (P. tremula x tremuloides), representative of each leaf type (bifacial and isobilateral, respectively). Poplar orthologs of AS1 have significantly higher expression in aspen leaf blade and lower in the petiole, suggestive of a potential role in the isobilateral leaf phenotype consistent with the previously observed phenotypes. Furthermore, an ABERRANT TESTA SHAPE (ATS) ortholog has significantly lower expression in aspen leaf tissue, also suggesting a possible contribution of this gene to abaxial greening.
authors.affiliation: Department of Biological Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, ON, M1C 1A4, Canada. nowakj3@gmail.com.
authors.forename: Julia S
authors.initials: JS
authors.lastname: Nowak
authors.affiliation: Botany Department, University of British Columbia, 3529-6270 University Blvd., Vancouver, BC, V6T 1Z4, Canada. carl.douglas@ubc.ca.
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Douglas
authors.affiliation: Botany Department, University of British Columbia, 3529-6270 University Blvd., Vancouver, BC, V6T 1Z4, Canada. quentin.cronk@ubc.ca.
authors.forename: Quentin C B
authors.initials: QC
authors.lastname: Cronk
keywords: ASYMMETRIC LEAVES1; KANADI; Populus tremula x tremuloides; Populus trichocarpa; abaxial greenness; adaxial–abaxial polarity; leaf blade