Title : Regulation of compound leaf development in Medicago truncatula
Abstract:
Leaf development requires highly regulated cell proliferation, differentiation and expansion patterns. As a model legume species, Medicago truncatula exhibits the simplest form of compound leaves; a single terminal leaflet is developed on the distal end of rachis and a pair of lateral leaflets is developed on both sides of petiole. M. truncatula belongs to the Inverted Repeat Lacking Clade (IRLC) of legumes. In the IRLC species, the orthologs of Leafy function in place of KNOXI to regulate compound leaf development, implying that the regulation mechanism of leaf development in M. truncatula is different from that of other model species, such as Arabidopsis thaliana, Cardamine hirsuta and Solanum lycopersicum. In addition, M. truncatula displays nyctinastic leaf movement which is generated by the pulvinus. Such leaf movements are common in the legume family (Leguminoseae) and the wood sorrel family (Oxalidaceae). By forward screening a large population of Tnt1 retrotransposon-tagged mutants of M. truncatula, we have identified several mutants that exhibited defects in leaf development and characterized the corresponding genes. More mutants with leaf developmental defects are being characterized to accelerate the understanding of the elaboration of compound leaves in M. truncatula.
Recently, we identified a novel pathway modulated by PINNA1 for the transition from trifoliate to pinnatelike pentafoliate leaves in M.truncatula. We found that mutations in PINNA1 led to the formation of ectopic leaflets in pinnately compound leaves, and the pentafoliate leaf in pinnna1 results from the activation of MtKNOXI. Genetic and biochemical analysis showed that PINNA1 has dual repression of KNOXI function in M. truncatula. PINNA1 represses the expression of MtKNOXI in leaf primordia, while PINNA1 interacts with MtKNOXI and sequesters it to the cytoplasm. Further investigations reveal that Unusual Floral Organs (MtUFO) is the direct target of MtKNOXI, and mediates the transition from trifoliate to pinnatelike pentafoliate leaves. This study provides insights in the compound leaf complexity controlling by the conserved and diverged molecular mechanisms.
Audience Take Away Notes
- Leguminous plants play essential roles in ecosystems, including nitrogen fixation and soil enrichment. Understanding leaf development in legumes contributes to our knowledge of plant diversity. By studying leaf development, we gain insights into legume adaptation and ecological interactions. Moreover, Educators can use examples from M. truncatula to illustrate fundamental concepts of leaf development in plant biology courses. By comparing and contrasting M. truncatula with other model species (e.g., Arabidopsis thaliana), students gain a deeper understanding of the diversity of leaf forms and the underlying genetic processes. The audience can use their understanding of leaf development in M. truncatula to enhance crop productivity, advance biotechnological applications, educate others, and contribute to environmental stewardship.
