Department of Biological Sciences, University of Toronto Scarborough, Toronto M1C 1A4, Canada.
Department of Cell and Systems Biology, University of Toronto, Toronto M5S 3G5, Canada.
J Exp Bot. 2017 Mar 1;68(7):1555-1567. doi: 10.1093/jxb/erx046.
FUSCA3 (FUS3) is a short-lived B3-domain transcription factor that regulates seed development and phase transitions in Arabidopsis thaliana. The mechanisms controlling FUS3 levels are currently poorly understood. Here we show that FUS3 interacts with the RING E3 ligase ABI3-INTERACTING PROTEIN2 (AIP2). AIP2-green fluorescent protein (GFP) is preferentially expressed in the protoderm during early embryogenesis, similarly to FUS3, suggesting that their interaction is biologically relevant. FUS3 degradation is delayed in the aip2-1 mutant and FUS3-GFP fluorescence is increased in aip2-1, but only during mid-embryogenesis, suggesting that FUS3 is negatively regulated by AIP2 at a specific time during embryogenesis. aip2-1 shows delayed flowering and therefore also functions post-embryonically to regulate developmental phase transitions. Plants overexpressing FUS3 post-embryonically in the L1 layer (ML1p:FUS3) show late flowering and other developmental phenotypes that can be rescued by ML1p:AIP2, further supporting a negative role for AIP2 in FUS3 accumulation. However, additional factors regulate FUS3 levels during embryogenesis, as ML1:AIP2 seeds do not resemble fus3-3. Lastly, targeted expression of a RING-inactive AIP2 variant to the protoderm/L1 layer causes FUS3 and ABI3 overexpression phenotypes and defects in cotyledon development. Taken together, these results indicate that AIP2 targets FUS3 for degradation and plays a role in cotyledon development and flowering time in Arabidopsis.
FUSCA3（FUS3）是一种短寿命的 B3 结构域转录因子，它调节拟南芥的种子发育和阶段转变。目前，控制 FUS3 水平的机制还知之甚少。在这里，我们表明 FUS3 与 RING E3 连接酶 ABI3-INTERACTING PROTEIN2（AIP2）相互作用。AIP2-绿色荧光蛋白（GFP）在早期胚胎发生过程中优先在原表皮中表达，与 FUS3 相似，这表明它们的相互作用具有生物学意义。AIP2-1 突变体中 FUS3 的降解被延迟，并且 AIP2-1 中 FUS3-GFP 的荧光增加，但仅在中期胚胎发生期间，这表明 FUS3 在胚胎发生过程中的特定时间被 AIP2 负调控。aip2-1 表现出开花延迟，因此也在胚胎后时期发挥作用以调节发育阶段转变。在 L1 层（ML1p：FUS3）中胚胎后过表达 FUS3 的植物表现出开花延迟和其他发育表型，这些表型可以被 ML1p：AIP2 挽救，进一步支持 AIP2 在 FUS3 积累中的负作用。然而，在胚胎发生期间，其他因素调节 FUS3 水平，因为 ML1：AIP2 种子与 fus3-3 不同。最后，将一种无活性的 RING 结构域 AIP2 变体靶向原表皮/L1 层会导致 FUS3 和 ABI3 过表达表型以及子叶发育缺陷。总之，这些结果表明 AIP2 将 FUS3 靶向降解，并在拟南芥的子叶发育和开花时间中发挥作用。
