The role of KNOX genes during simple and compound leaf development in the genus Ampelopsis (Vitaceae)

The grape family (Vitaceae) is a large group of plants consisting of approximately 900 species. Cultivated grapes (Vitis vinifera L.) are the most famous species in the Vitaceae family because of their economic importance in both fruit and wine production. In the U.S. alone, 7.4 million tons of grapes were produced in 2010 (www.nass.usda.gov) equating to approximately $162 billion annually (www.ngwi.org), making it one of the most economically important fruit crops in the country. It is generally supported, through molecular analyses, that Vitaceae is a sister to all other Rosids, a related group comprising over one fourth of the world’s flowering plants (Ren et al., 2007). This large group was found to have split from the rest of the flowering plants very early in plant evolution (Wang et al., 2007). Thus, a better understanding of the biology of grapes has the potential to improve our understanding of the biology of other rosid crops such as legumes (e.g. soybeans), fruit crops (e.g. apples), and oilseed crops (e.g. canola). The genus Ampelopsis, a member of the Vitaceae (grape) family, encompasses species that exhibit a wide range of mature leaf shape that vary from simple (undivided single blade) to compound (subdivided multiple blade unit). The purpose of this study was to investigate the involvement of KNOX-genes, specifically KNOX1 (Knotted1-like homeobox), in the development of Ampelopsis, and how this gene controls leaf morphology. Since virtually nothing is known about leaf development in the genus Ampelopsis, and Vitaceae as a whole, five species with various leaf shapes (simple, lobed, dissected and compound) were selected for the study: Ampelopsis aconitifolia, Ampelopsis arborea, Ampelopsis cordata, Ampelopsis glandulosa, and Ampelopsis humulifolia. Immunolocalizations of Knotted1 (KN1) antibody on paraffin sections of Ampelopsis shoot apical meristems were used to locate KNOX1 proteins. We found that during simple leaf development, KNOX1 was required for the initiation of leaf primordia in the shoot apical meristem, but was downregulated after emerging from the apex allowing the blade to remain undivided. However, in the compound-leafed species, KNOX1 expression persisted into young developing leaves to form leaflets, therefore, playing a role in leaf compounding. Overall, by assessing the role of KNOX genes and its regulation on leaf morphology, our study begins to assess how leaf shape separated into distinct groups within this genus during leaf evolution as well as give us clues into the evolutionary history of the ancestral leaf form