ARC Centre of Excellence for Plant Energy Biology, The University of Western Australia, Crawley, WA 6009, Australia.
Development. 2012 Apr;139(7):1285-95. doi: 10.1242/dev.074567. Epub 2012 Feb 22.
Karrikins are butenolides derived from burnt vegetation that stimulate seed germination and enhance seedling responses to light. Strigolactones are endogenous butenolide hormones that regulate shoot and root architecture, and stimulate the branching of arbuscular mycorrhizal fungi. Thus, karrikins and strigolactones are structurally similar but physiologically distinct plant growth regulators. In Arabidopsis thaliana, responses to both classes of butenolides require the F-box protein MAX2, but it remains unclear how discrete responses to karrikins and strigolactones are achieved. In rice, the DWARF14 protein is required for strigolactone-dependent inhibition of shoot branching. Here, we show that the Arabidopsis DWARF14 orthologue, AtD14, is also necessary for normal strigolactone responses in seedlings and adult plants. However, the AtD14 paralogue KARRIKIN INSENSITIVE 2 (KAI2) is specifically required for responses to karrikins, and not to strigolactones. Phylogenetic analysis indicates that KAI2 is ancestral and that AtD14 functional specialisation has evolved subsequently. Atd14 and kai2 mutants exhibit distinct subsets of max2 phenotypes, and expression patterns of AtD14 and KAI2 are consistent with the capacity to respond to either strigolactones or karrikins at different stages of plant development. We propose that AtD14 and KAI2 define a class of proteins that permit the separate regulation of karrikin and strigolactone signalling by MAX2. Our results support the existence of an endogenous, butenolide-based signalling mechanism that is distinct from the strigolactone pathway, providing a molecular basis for the adaptive response of plants to smoke.
卡里卡丁是一种来源于燃烧植物的丁烯内酯，它能刺激种子发芽，并增强幼苗对光的响应。独脚金内酯是一种内源性的丁烯内酯激素，它调节着地上部和地下部的架构，并刺激丛枝菌根真菌的分枝。因此，卡里卡丁和独脚金内酯在结构上相似，但在生理上是不同的植物生长调节剂。在拟南芥中，对这两类丁烯内酯的响应都需要 F-box 蛋白 MAX2，但尚不清楚如何实现对卡里卡丁和独脚金内酯的离散响应。在水稻中，DWARF14 蛋白是独脚金内酯依赖性抑制分枝所必需的。在这里，我们表明，拟南芥 DWARF14 同源物 AtD14 也需要正常的独脚金内酯响应在幼苗和成年植物中。然而，AtD14 同源物 KARRIKIN INSENSITIVE 2 (KAI2) 是对卡里卡丁的响应所必需的，而不是对独脚金内酯的响应。系统发育分析表明 KAI2 是祖先的，而 AtD14 功能的特化是随后进化而来的。Atd14 和 kai2 突变体表现出 max2 表型的不同子集，AtD14 和 KAI2 的表达模式与在植物发育的不同阶段对独脚金内酯或卡里卡丁的响应能力一致。我们提出 AtD14 和 KAI2 定义了一类蛋白质，它们允许 MAX2 对卡里卡丁和独脚金内酯信号进行单独调节。我们的结果支持存在一种内源性的、基于丁烯内酯的信号机制，它与独脚金内酯途径不同，为植物对烟雾的适应性反应提供了分子基础。
