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

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.

Reducing shade avoidance can improve Arabidopsis canopy performance against competitors

The loss of crop yield due to weeds is an urgent agricultural problem. Although herbicides are an effective way to control weeds, more sustainable solutions for weed management are desirable. It has been proposed that crop plants can communally suppress weeds by shading them out. Shade avoidance responses, such as upward leaf movement (hyponasty) and stem or petiole elongation, enhance light capture of individual plants, increasing their individual fitness. The shading capacity of the entire crop community might, however, be more effective if aspects of shade avoidance are suppressed. Testing this hypothesis in crops is hampered by the lack of well-characterized mutants. We therefore investigated if Arabidopsis competitive performance at the community level against invading competitors is affected by the ability to display shade avoidance. We tested two mutants: pif4pif5 that has mildly reduced petiole elongation and hyponasty and pif7 with normal elongation but absent hyponasty in response to shade. Although pif4pif5 performed similar to wildtype, we found that pif7 showed significantly increased canopy biomass and suppression of invading competitors as compared to its wildtype. Our data thus show that modifying specific shade avoidance aspects has potential for plant community performance. This may help to suppress weeds in crop stands.HighlightHyponastic response in canopies facilitates light penetration and weed growth. Inhibition of this response to neighbors increased canopy biomass, canopy closure and suppression of competitors.