ASYMMETRIC LEAVES2-LIKE15 gene, a member of AS2/LOB family, shows a dual abaxializing or adaxializing function in Arabidopsis lateral organs

In determining leaf adaxial fates, Arabidopsis ASYMMERTIC LEAVES1 (AS1) and AS2/LBD6 are essential. The Arabidopsis ASYMMETRIC LEAVES2-LIKE15/LBD17 gene, one member of the LATERAL ORGAN BOUNDARY DOMAIN gene family, is expressed at the base of juvenile lateral roots, as well as in boundaries between meristems and organ primordial. For better comprehending the function of ASL15/LBD17 in the Arabidopsis development, its antisense-expression construct was constructed, and some 35S:ASL15/LBD17 transgenic plants that were antisense overexpression mutants were attained. The transgenic plants can specify either abaxial or adaxial cell fate in differently shaped rosette leaves. In detail, slightly and extremely narrow rosette leaves (class I) displayed abaxial cell traits, compared with those of Col-0. Inflorescence stems of these transgenic plants also showed abaxial organ identity. Both radial needle-like and filamentous symmetric rosette leaves (class II) presented adaxial cell fate, in contrast to those of wild type (Col-0). However, in the background of AS2 mutation, antisense 35S: ASL15 only presented abaxial organ identity, implying that the influences of antisense 35: ASL15 require a functional AS2 gene. In addition, antisense 35S: ASL15 was defective in proximodistal patterning. In addition, antisense 35S: ASL15 lead to the enhancement of the transcript levels of the KNOX genes, i.e., KNAT2, KNAT6, and STM, but not of the related KNAT1 gene. Taken together, our findings show that ASL15/LBD17 has a dual abaxializing or adaxializing function, and is also related to distal and proximal patterning in the lateral organs of Arabidopsis. Therefore, ASL15/LBD17 has multiple functions in the Arabidopsis development.