The F-box protein MIO1/SLB1 regulates organ size and leaf movement in Medicago truncatula

Abstract

The size of leaf and seed organs, determined by the interplay of cell proliferation and expansion, is closely related to the final yield and quality of forage and crops. Yet the cellular and molecular mechanisms underlying organ size modulation remain poorly understood, especially in legumes. Here, MINI ORGAN1 (MIO1) was identified as a key regulator of organ size, which encodes an F-box protein (SLB1) was recently reported to control lateral branching in M. truncatula. We show that loss of function of MIO1/SLB1 severely reduced organ size. Conversely, plants with overexpression of MIO1/SLB1 plants had enlarged organs. Cellular analysis revealed that MIO1/SLB1 controlled organ size mainly by modulating primary cell proliferation during the early stages of leaf development. Biochemistry analysis revealed MIO1/SLB1 could form part of an SKP1/Cullin/F-box (SCF) E3 ubiquitin ligase complex, to target BIG SEEDS1 (BS1), a repressor of primary cell division for degradation. Interestingly, we found that MIO1/SLB1 also played a key role in pulvinus development and leaf movement by modulating cell proliferation of the pulvinus as leaves developed. Our study not only demonstrates a conserved role of MIO1/SLB1 for organ size control in legumes, but also sheds light on the novel function of MIO1/SLB1 in leaf movement.

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

“…Several factors have been reported to influence the leaf movement. For example, the F-box protein MIO1/SLB1, a component of the SKP1/Cullin/F-box (SCF) E3 ubiquitin ligase complex, influences leaf movement through possibly controlling the length of the pulvinus [ 64 ]. Aquaporins, anion channels, and K + channels are thought to regulate volume changes of the motor cells and thus control leaf movement [ 18 , 65 , 66 ].…”

The Genetic Control of the Compound Leaf Patterning in Medicago truncatula

“…In young leaves, the MtWUS was slightly expressed in the leaf lamina as a whole, but it was considered at the tips of the marginal serrations. The MIO1 / SLB1 encodes an F-box protein, an ortholog of A. thaliana STERILE APETALA (SAP) ( Yin et al, 2020 ; Zhou et al, 2021 ). The loss-of-function of MIO1/SLB1 severely reduced organ size.…”

“…As mentioned above, the F-box protein MIO1/SLB1 plays a positive role in organ size determination. Plants overexpressing MIO1/SLB1 had enlarged organs, and this is because MIO1/SLB1 forms part of SKP1/Cullin/F-box (SCF) E3 ubiquitin ligase complex, targeting BS1 proteins for degradation ( Yin et al, 2020 ; Zhou et al, 2021 ). The pathway of BS1 and MIO1/SLB1 may mainly modulate primary cell proliferation during the early stages of leaf development to control the leaf size.…”

“…Considering that the ELP1/PLP and its orthologs are highly homologous to the Arabidopsis LOB protein which has been shown to directly up-regulates the BR metabolic gene phyB Activation-tagged Suppressor1-dominant ( BAS1 ), further efforts are needed to determine whether BR accumulation is involved in pulvinus development and what roles ELP1/PLP and its orthologs play in this process. The F-box protein MIO1/SLB1 is another factor necessary for robust pulvinus development ( Zhou et al, 2021 ). The pulvini of mio1/slb1 mutants were shortened even completely absent from the base of its leaflets, leading to a reduced degree of leaflet rotation or a completely impaired leaf movement.…”

The Organ Size and Morphological Change During the Domestication Process of Soybean

“…Down-regulation of soybean BS1 gene significantly increased the size and weight of seeds and leaves ( Ge et al, 2016 ). SLB1/MIO1 encodes an Arabidopsis thaliana F-box protein SAP homologous in Medicago truncatula ( Zhou et al, 2021 ). SLB1 interacts with BS1 to control organ size, and overexpression of SLB1 leads to the increased seed and leaf size in soybean ( Yin et al, 2020 ).…”