Brassinosteroid homeostasis is critical for the functionality of the Medicago truncatula pulvinus

Abstract

Many plant species open their leaves during the daytime and close them at night as if sleeping. This leaf movement is known as nyctinasty, a unique and intriguing phenomenon that been of great interest to scientists for centuries. Nyctinastic leaf movement occurs widely in leguminous plants, and is generated by a specialized motor organ, the pulvinus. Although a key determinant of pulvinus development, PETIOLULE-LIKE PULVINUS (PLP), has been identified, the molecular genetic basis for pulvinus function is largely unknown. Here, through an analysis of knockout mutants in barrelclover (Medicago truncatula), we showed that neither altering brassinosteroid (BR) content nor blocking BR signal perception affected pulvinus determination. However, BR homeostasis did influence nyctinastic leaf movement. BR activity in the pulvinus is regulated by a BR-inactivating gene PHYB ACTIVATION TAGGED SUPPRESSOR1 (BAS1), which is directly activated by PLP. A comparative analysis between M. truncatula and the non-pulvinus forming species Arabidopsis and tomato (Solanum lycopersicum) revealed that PLP may act as a factor that associates with unknown regulators in pulvinus determination in M. truncatula. Apart from exposing the involvement of BR in the functionality of the pulvinus, these results have provided insights into whether gene functions among species are general or specialized.

Combining Fine Mapping, Whole-Genome Re-Sequencing, and RNA-Seq Unravels Candidate Genes for a Soybean Mutant with Short Petioles and Weakened Pulvini

“…Interestingly, a recent study showed that the geometry of the compound leaf is important for leaf movement in Medicago truncatula [ 67 ]. Moreover, the plant hormone BR homeostasis is critical for nyctinastic leaf movement but has no effect on pulvinus determination [ 68 ]. In this study, the KEGG pathway enrichment analysis showed that the DEGs were highly enriched in BR biosynthesis ( Figure S2 ).…”

Mechanics of Reversible Deformation during Leaf Movement and Regulation of Pulvinus Development in Legumes

“…Brassinosteroids are also becoming known as regulators of pulvinar development downstream of the ELP1/PLP pathway. Kong et al found that overexpression of ELP1/PLP activated the expression of BAS1, an inhibitor of brassinosteroid biosynthesis, indicating that the brassinosteroid signaling pathway played a role downstream of ELP1/PLP [ 23 ]. Through forward genetics, Zhao et al obtained a nyctinastic movement-deficient mutant of M. truncatula , mtdwf4 [ 24 ].…”

The Genetic Control of the Compound Leaf Patterning in Medicago truncatula

“…Brassinosteroids Insensitive 1 ( BRI1 ) is required for BR perception and initiation of subsequent signal transduction in Arabidopsis ( Li and Chory, 1997 ). In Medicago, the loss-of-function mutant of MtBRI1 has typical BR-deficient phenotypes of extreme dwarfness and infertility, and its leaves were thickened, curled, dark green, and greatly reduced in size with the petioles and rachises failed to elongate ( Cheng et al, 2017 ; Kong et al, 2021 ). MtDWARF4A ( MtDWF4A ), a gene encoding a cytochrome P450 protein orthologous to A. thaliana DWARF4, is required for the BR biosynthesis.…”

“…MtDWARF4A ( MtDWF4A ), a gene encoding a cytochrome P450 protein orthologous to A. thaliana DWARF4, is required for the BR biosynthesis. The mtdwf4a mutant exhibits mild BR-deficient phenotypes, semi-dwarfism, short petioles, and rachis, but normal fertility ( Kong et al, 2021 ; Zhao et al, 2021 ). The MtDWF4A has a highly homologous copy designated as MtDWF4B , it will be critical to explore the possibilities of functional redundancy and diversification between MtDWF4A and MtDWF4B in the BR biosynthetic pathways ( Zhao et al, 2021 ).…”