Isolation and expression patterns of LATERAL ORGAN BOUNDARIES-like genes in Lotus japonicus

A shoot apical meristem (SAM) is composed of several distinct domains and lateral organs are initiated at the peripheral zone during plant development. Establishment and maintenance of boundary between SAM and lateral organs is an important developmental process, in which many regulators are involved. LATERAL ORGAN BOUNDARIES (LOB) in Arabidopsis, displaying a specific expression pattern corresponding to the boundary of developmental lateral organs, belongs to a large gene family--LOB domain gene family, which encode proteins with a conserved LOB domain at the N-terminus. Beside LOB, other members of this gene family are also involved in divergent developmental processes in Arabidopsis. To investigate the functions of LOB-like genes in the distantly related legumes, we isolated LjLOBs from a model legume plant Lotus japonicus, and conducted RNA in situ hybridization to investigate their expression patterns. It was found that LjLOB1 and LjLOB3 were strongly expressed at the bases of leaflet primordia, which coincided with the boundaries between leaflet primordia and compound leaf meristem, while LjLOB4 was expressed at the boundaries between whorls in the developing floral bud. The different special expression patterns of LjLOBs strongly suggest that their functions in L. japonicus may be divergent: LjLOB1 and LjLOB3 could play important roles in the control of compound leaf development, and LjLOB4 may be required during floral development.