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Abstract
Class I KNOTTED-like homeobox (KNOXI) genes are critical for the maintenance of the shoot apical meristem. The expression domain of KNOXI is regulated by ASYMMETRIC LEAVES1/ROUGHSHEATH2/PHANTASTICA (ARP) genes, which are associated with leaf morphology. In the inverted repeat-lacking clade (IRLC) of Fabaceae, the orthologs of LEAFY (LFY) function in place of KNOXI to regulate compound leaf development. Here, we characterized loss-of-function mutants of ARP (PHAN) and SHOOTMERISTEMLESS (STM)- and BREVIPEDICELLUS (BP)-like KNOXI in the model IRLC legume species Medicago truncatula. The function of ARP genes is species specific. The repression of STM/BP-like KNOXI genes in leaves is not mediated by PHAN, and no suppression of PHAN by STM/BP-like KNOXI genes was observed either, indicating that STM/BP-like KNOXI genes are uncoupled from PHAN in M. truncatula. Furthermore, comparative analyses of phenotypic output in response to ectopic expression of KNOXI and the M. truncatula LFY ortholog, SINGLE LEAFLET1 (SGL1), reveal that KNOXI and SGL1 regulate parallel pathways in leaf development. We propose that SGL1 probably functions in a stage-specific manner in the regulation of the indeterminate state of developing leaves in M. truncatula.
Highlights
KNOTTED-like homeobox (KNOX) proteins regulate both embryonic and postembryonic development in plants
The KNOXI gene family from Arabidopsis thaliana consists of SHOOTMERISTEMLESS (STM), BREVIPEDICELLUS (BP)/ KNOTTED-like in A. thaliana 1 (KNAT1), KNAT2, and KNAT6 (Lincoln et al, 1994; Long et al, 1996)
We show that M. truncatula ASYMMETRIC LEAVES1/ROUGHSHEATH2/PHANTASTICA (ARP) (PHAN) and STM/BP-like KNOXI genes exhibit conserved functions
Summary
KNOTTED-like homeobox (KNOX) proteins regulate both embryonic and postembryonic development in plants. KNOX genes fall into two subclasses, Class I KNOX (KNOXI) and Class II KNOX (KNOXII) based on sequence similarity, gene structure, and expression pattern (Hay and Tsiantis, 2010). KNOXI genes, which are evolutionarily close to maize (Zea mays) KN1 (Vollbrecht et al, 1991), are expressed in the shoot apical meristem (SAM) of both monocot and eudicot plants and play crucial roles in the maintenance of SAM and regulation of leaf complexity across vascular plants (Long et al, 1996; Hake et al, 2004; Barkoulas et al, 2008; Hay and Tsiantis, 2010). KNOXII genes display diverse expression patterns, and their function is not clear (Serikawa et al, 1997; Byrne et al, 2002).
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