Plant Development and (Epi)Genetics, Swammerdam Institute for Life Science, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, the Netherlands.
Department of Agricultural, Food and Environmental Sciences, University of Perugia, Borgo XX Giugno 74, 06121 Perugia, Italy.
Cell Rep. 2021 Sep 28;36(13):109749. doi: 10.1016/j.celrep.2021.109749.
Homologous ("canonical") RAB5 proteins regulate endosomal trafficking to lysosomes in animals and to the central vacuole in plants. Epidermal petal cells contain small vacuoles (vacuolinos) that serve as intermediate stations for proteins on their way to the central vacuole. Here, we show that transcription factors required for vacuolino formation in petunia induce expression of RAB5a. RAB5a defines a previously unrecognized clade of canonical RAB5s that is evolutionarily and functionally distinct from ARA7-type RAB5s, which act in trafficking to the vacuole. Loss of RAB5a reduces cell height and abolishes vacuolino formation, which cannot be rescued by the ARA7 homologs, whereas constitutive RAB5a (over)expression alters the conical cell shape and promotes homotypic vacuolino fusion, resulting in oversized vacuolinos. These findings provide a rare example of how gene duplication and neofunctionalization increased the complexity of membrane trafficking during evolution and suggest a mechanism by which cells may form multiple vacuoles with distinct content and function.
同源（“规范”）RAB5 蛋白在动物中调节内体向溶酶体的运输，在植物中调节中央液泡的运输。表皮花瓣细胞含有小液泡（液泡小泡），它们是蛋白质向中央液泡运输过程中的中间站。在这里，我们表明，用于矮牵牛液泡小泡形成的转录因子诱导 RAB5a 的表达。RAB5a 定义了一个以前未被识别的规范 RAB5 家族，它在进化和功能上与在液泡运输中起作用的 ARA7 型 RAB5 不同。RAB5a 的缺失会降低细胞高度并消除液泡小泡的形成，而 ARA7 同源物不能挽救这一过程，而组成型 RAB5a（过度）表达会改变锥形细胞形状并促进同源液泡小泡融合，导致液泡小泡过大。这些发现为基因复制和新功能化如何在进化过程中增加膜运输的复杂性提供了一个罕见的例子，并提出了一种细胞可能形成具有不同内容和功能的多个液泡的机制。
