Abstract
Many studies suggest that there are distinct regulatory processes controlling compound leaf development in different clades of legumes. Loss of function of the LEAFY (LFY) orthologs results in a reduction of leaf complexity to different degrees in inverted repeat-lacking clade (IRLC) and non-IRLC species. To further understand the role of LFY orthologs and the molecular mechanism in compound leaf development in non-IRLC plants, we studied leaf development in unifoliate leaf (un) mutant, a classical mutant of mungbean (Vigna radiata L.), which showed a complete conversion of compound leaves into simple leaves. Our analysis revealed that UN encoded the mungbean LFY ortholog (VrLFY) and played a significant role in leaf development. In situ RNA hybridization results showed that STM-like KNOXI genes were expressed in compound leaf primordia in mungbean. Furthermore, increased leaflet number in heptafoliate leaflets1 (hel1) mutants was demonstrated to depend on the function of VrLFY and KNOXI genes in mungbean. Our results suggested that HEL1 is a key factor coordinating distinct processes in the control of compound leaf development in mungbean and its related non-IRLC legumes.
Highlights
Plant leaves are the primary photosynthetic organs that are initiated on the flanks of the shoot apical meristem (SAM)
In most compound-leafed species, activation of KNOXI gene expression in the leaf primordia is correlated with the development of compound leaves[6,12]
In inverted repeat-lacking clade (IRLC) legume species with compound leaves such as pea and M. truncatula, the STM/BP-like KNOXI genes are excluded from the leaf primordia, and their expression is not correlated with compound leaf development[11,12,13]
Summary
Plant leaves are the primary photosynthetic organs that are initiated on the flanks of the shoot apical meristem (SAM). The class I KNOTTED1-like homeobox (KNOXI) genes are involved in the maintenance of the meristem activity of SAM, while the initiation of leaves requires downregulation of KNOXI genes at the incipient site[1,2,3]. In simple-leafed species such as Arabidopsis thaliana, downregulation of KNOXI genes in leaf primordia is permanent, whereas in most compound-leafed eudicot species, including the tomato (Solanum lycopersicum) and Cardamine hirsuta, KNOXI genes are reactivated in leaf primordia after initiation of leaf development[4,5,6]. Genetic analysis shows that single mutants, double mutants and triple mutants of 3 STM/BP-like KNOXI genes, namely, MtKNOX1, MtKNOX2, and MtKNOX6, in M. truncatula do not show obvious defects in compound leaves[13].
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