RESUMEN
Karrikins (KARs) are butenolides found in smoke that can influence germination and seedling development of many plants. The KAR signaling mechanism is hypothesized to be very similar to that of the plant hormone strigolactone (SL). Both pathways require the F-box protein MORE AXILLARY GROWTH2 (MAX2), and other core signaling components have shared ancestry. Putatively, KAR activates the receptor KARRIKIN INSENSITIVE2 (KAI2), triggering its association with the E3 ubiquitin ligase complex SCFMAX2 and downstream targets SUPPRESSOR OF MAX2 1 (SMAX1) and SMAX1-LIKE2 (SMXL2). Polyubiquitination and proteolysis of SMAX1 and SMXL2 then enable growth responses to KAR. However, many of the assumptions of this model have not been demonstrated. Therefore, we investigated the posttranslational regulation of SMAX1 from the model plant Arabidopsis (Arabidopsis thaliana). We find evidence that SMAX1 is degraded by KAI2-SCFMAX2 but is also subject to MAX2-independent turnover. We identify SMAX1 domains that are responsible for its nuclear localization, KAR-induced degradation, association with KAI2, and ability to interact with other SMXL proteins. KAI2 undergoes MAX2-independent degradation after KAR treatment, which we propose results from its association with SMAX1 and SMXL2. Finally, we discover an SMXL domain that mediates receptor-target interaction preferences in KAR and SL signaling, laying the foundation for understanding how these highly similar pathways evolved to fulfill different roles.
Asunto(s)
Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/metabolismo , Furanos/farmacología , Hidrolasas/metabolismo , Péptidos y Proteínas de Señalización Intracelular/química , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Proteolisis , Piranos/farmacología , Secuencias de Aminoácidos , Proteínas Portadoras/metabolismo , Núcleo Celular/efectos de los fármacos , Núcleo Celular/metabolismo , Secuencia Conservada , Proteínas Fluorescentes Verdes/metabolismo , Compuestos Heterocíclicos con 3 Anillos/farmacología , Hidrolasas/química , Lactonas/farmacología , Extractos Vegetales , Unión Proteica/efectos de los fármacos , Dominios Proteicos , Transporte de Proteínas/efectos de los fármacos , Proteolisis/efectos de los fármacos , Eliminación de Secuencia , Relación Estructura-Actividad , Nicotiana/efectos de los fármacosRESUMEN
Karrikins and strigolactones are novel plant growth regulators that contain similar molecular features, but very little is known about how they elicit responses in plants. A tentative molecular mechanism has previously been proposed involving a Michael-type addition for both compounds. Through structure-activity studies with karrikins, we now propose an alternative mechanism for karrikin and strigolactone mode of action that involves hydrolysis of the butenolide ring.
Asunto(s)
Furanos/farmacología , Lactonas/metabolismo , Reguladores del Crecimiento de las Plantas/farmacología , Piranos/farmacología , Sitios de Unión , Simulación por Computador , Furanos/química , Germinación/efectos de los fármacos , Lactonas/química , Reguladores del Crecimiento de las Plantas/química , Proteínas de Plantas/química , Proteínas de Plantas/metabolismo , Estructura Terciaria de Proteína , Piranos/química , Semillas/metabolismo , Solanum/crecimiento & desarrollo , Solanum/metabolismo , Relación Estructura-ActividadRESUMEN
Karrikinolide is a naturally derived potent seed germination stimulant that is responsible for triggering the germination of numerous plant species from various habitats around the world. We now report that solar irradiation of karrikinolide yields two novel head-to-head cage photodimers with the formation, stability and bioactivity of both presented herein.