KNAT6: AnArabidopsisHomeobox Gene Involved in Meristem Activity and Organ Separation

Abstract

The homeobox gene family plays a crucial role during the development of multicellular organisms. The KNOTTED-like genes from Arabidopsis thaliana (KNAT6 and KNAT2) are close relatives of the meristematic genes SHOOT MERISTEMLESS (STM) and BREVIPEDICELLUS, but their function is not currently known. To investigate their role, we identified null alleles of KNAT6 and KNAT2. We demonstrate that KNAT6 contributes redundantly with STM to the maintenance of the shoot apical meristem (SAM) and organ separation. Consistent with this role, the expression domain of KNAT6 in the SAM marks the boundaries between the SAM and cotyledons. The lack of meristematic activity in the knat6 stm-2 double mutant and the fusion of cotyledons were linked to the modulation of CUP-SHAPED COTYLEDON (CUC) activity. During embryogenesis, KNAT6 is expressed later than STM and CUC. In agreement with this fact, CUC1 and CUC2 were redundantly required for KNAT6 expression. These data provide the basis for a model in which KNAT6 contributes to SAM maintenance and boundary establishment in the embryo via the STM/CUC pathway. KNAT2, although the closest related member of the family to KNAT6, did not have such a function.

Transcriptomic Analyses Indicate That Maize Ligule Development Recapitulates Gene Expression Patterns That Occur during Lateral Organ Initiation

“…KNAT6 is expressed at organ boundaries and contributes to boundary establishment via interactions with the KNOX protein SHOOT-MERISTEMLESS1 and with CUC (Belles-Boix et al, 2006). We speculate that LG3 may have a similar function during boundary establishment in maize.…”

KNOX genes: versatile regulators of plant development and diversity

“…BP shares aspects of both these gene expression patterns in the SAM during postembryonic development (its embryonic expression marks the hypocotyl), whereas KNAT2 is expressed during embryogenesis and marks the base of the SAM (Byrne et al, 2002;Dockx et al, 1995). Genetic redundancy masks the contribution of KNAT6 and BP, which act, in addition to STM, to maintain SAM activity and organ separation (Belles-Boix et al, 2006;Byrne et al, 2002).…”

“…STM is the first KNOX gene expressed during early embryogenesis and its expression marks the entire SAM (Long et al, 1996). KNAT6 is expressed in the embryonic SAM once bilateral symmetry is established and later marks the SAM boundaries (Belles-Boix et al, 2006). BP shares aspects of both these gene expression patterns in the SAM during postembryonic development (its embryonic expression marks the hypocotyl), whereas KNAT2 is expressed during embryogenesis and marks the base of the SAM (Byrne et al, 2002;Dockx et al, 1995).…”

Interaction ofKNAT6andKNAT2withBREVIPEDICELLUSandPENNYWISEinArabidopsisInflorescences

“…BP contributes with STM to SAM maintenance since the loss of function of BP reduces the residual meristematic activity of the weak allele stm-2 (Byrne et al, 2002(Byrne et al, , 2003. Like BP, KNAT6 contributes redundantly with STM to SAM function, as the inactivation of KNAT6 abolishes the meristematic potential of the weak allele stm-2 (Belles- Boix et al, 2006). In addition, a specific role for KNAT6 in boundary maintenance is indicated by a severe defect in cotyledon separation observed in the stm-2 knat6 double mutant (Belles-Boix et al, 2006).…”

“…Like BP, KNAT6 contributes redundantly with STM to SAM function, as the inactivation of KNAT6 abolishes the meristematic potential of the weak allele stm-2 (Belles- Boix et al, 2006). In addition, a specific role for KNAT6 in boundary maintenance is indicated by a severe defect in cotyledon separation observed in the stm-2 knat6 double mutant (Belles-Boix et al, 2006). KNAT2 also is expressed in the SAM, but its role is unclear as its inactivation does not aggravate stm-2, knat6 stm-2, or knat6 bp stm-2 phenotypes (Belles-Boix et al, 2006).…”