A correlation between leaf shape and its related key genes in Viola albida complex

Abstract

Simple to compound leaves occur in the Viola albida complex, which comprises the simple, finely serrate leaves of V. albida Palib., the deeply lobed leaves of V. albida var. takahashii (Nakai) Nakai, and the compound leaves of Viola chaerophylloides (Regel) W. Becker. To identify a correlation between the different leaf forms and the expression of several key genes with roles in leaf morphogenesis, the distinct leaf forms occurring within these species were generated by tissue culture of the V. chaerophylloides petiole, for comparison with wild-type leaves. Compound leaves were generally formed from a petiole explant taken close to the leaf blade, whereas simple leaves resulted from petiole explants taken close to the petiole base. KNOTTED-1 (VaKN1), SHOOTMERISTEMLESS (VaSTM), CUP-SHAPED COTYLEDON-2 (VaCUC2), and ASYMMETRIC LEAVES 1 (VaAS1), which are known to play key roles during compound leaf patterning and morphogenesis, were isolated and multiple sequence alignment revealed that there was no sequence variation at the amino acid level within each gene and between the three varieties. Phylogenetic analysis confirmed that the isolated genes were homologous to KN, STM, CUC2, and AS1. The expression of VaKN1, VaSTM, and VaCUC2 was significantly elevated in the in vitro-cultured deeply lobed and compound leaves, as well as in V. chaerophylloides and V. albida var. takahashii plants, but was very low in the in vitro-cultured simple leaves and V. albida plants. These findings demonstrated that elevated transcripts of VaKN1, VaSTM, and VaCUC2 lead to the development of compound and deeply lobed leaves in the V. albida complex.