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Abstract
Molecular genetic studies suggest that FLORICAULA (FLO)/LEAFY (LFY) orthologs function to control compound leaf development in some legume species. However, loss-of-function mutations in the FLO/LFY orthologs result in reduction of leaf complexity to different degrees in Pisum sativum and Lotus japonicus. To further understand the role of FLO/LFY orthologs in compound leaf development in legumes, we studied compound leaf developmental processes and characterized a leaf development mutant, single leaflet1 (sgl1), from the model legume Medicago truncatula. The sgl1 mutants exhibited strong defects in compound leaf development; all adult leaves in sgl1 mutants are simple due to failure in initiating lateral leaflet primordia. In addition, the sgl1 mutants are also defective in floral development, producing inflorescence-like structures. Molecular cloning of SGL1 revealed that it encodes the M. truncatula FLO/LFY ortholog. When properly expressed, LFY rescued both floral and compound leaf defects of sgl1 mutants, indicating that LFY can functionally substitute SGL1 in compound leaf and floral organ development in M. truncatula. We show that SGL1 and LFY differed in their promoter activities. Although the SGL1 genomic sequence completely rescued floral defects of lfy mutants, it failed to alter the simple leaf structure of the Arabidopsis thaliana plants. Collectively, our data strongly suggest that initiation of lateral leaflet primordia required for compound leaf development involves regulatory processes mediated by the SGL1 function in M. truncatula.
Highlights
Molecular genetic studies suggest that FLORICAULA (FLO)/LEAFY (LFY) orthologs function to control compound leaf development in some legume species
In simple-leafed species, expression of the KNOX1 genes is permanently down-regulated in the initiating leaf primordia in a process that requires MYB domain transcription repressors ROUGH SHEATH2 (RS2) and ASYMMETRIC LEAVES1 (AS1) in maize and Arabidopsis, respectively, and involves hormonal signaling (Smith et al, 1992; Lincoln et al, 1994; Nishimura et al, 1999; Timmermans et al, 1999; Tsiantis et al, 1999; Byrne et al, 2000; Ori et al, 2000; Sakamoto et al, 2001; Hay et al, 2002; Hay et al, 2006; Uchida et al, 2007; Guo et al, 2008)
Molecular genetic studies suggest that regulatory processes leading to compound leaf development are more complex than that required for simple leaf development and involve multiple regulators such as the KNOX1 homeobox genes, the TCP class transcription factor Lanceolate, whose activity is in turn regulated by miR319 and perhaps other yet-to-be-identified regulators (Bharathan and Sinha, 2001; Bharathan et al, 2002; Brand et al, 2007; Jasinski et al, 2007; Ori et al, 2007)
Summary
Molecular genetic studies suggest that FLORICAULA (FLO)/LEAFY (LFY) orthologs function to control compound leaf development in some legume species. Molecular genetic studies indicate that the legume orthologs of the floral meristem (FM) identity gene FLORICAULA (FLO) from snapdragon (Antirrhinum majus) and LEAFY (LFY) from Arabidopsis, and their coregulators FIMBRIATA (FIM) and UNUSUAL FLORAL ORGAN (UFO), respectively, play a role in compound leaf development in compound-leafed legumes (Hofer et al, 1997; Hofer and Ellis, 1998; DeMason and Schmidt, 2001; Taylor et al, 2001; Dong et al, 2005). In transgenic soybean (Glycine max; outside of the IRLC) lines in which the endogenous LFY genes are down-regulated, the leaflet number is moderately reduced (Champagne et al, 2007) Taken together, these data support a significant role for the FLO/LFYand STP/ UFO orthologs in compound leaf development in some legumes and a minor role in others
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