School of Molecular Sciences, The University of Western Australia, 35 Stirling Hwy, Perth, WA, 6009, Australia.
Australian Research Council Centre of Excellence in Plant Energy Biology, The University of Western Australia, 35 Stirling Hwy, Perth, WA, 6009, Australia.
Nat Commun. 2020 Mar 9;11(1):1264. doi: 10.1038/s41467-020-14991-w.
Wildfires can encourage the establishment of invasive plants by releasing potent germination stimulants, such as karrikins. Seed germination of Brassica tournefortii, a noxious weed of Mediterranean climates, is strongly stimulated by KAR, the archetypal karrikin produced from burning vegetation. In contrast, the closely-related yet non-fire-associated ephemeral Arabidopsis thaliana is unusual because it responds preferentially to KAR. The α/β-hydrolase KARRIKIN INSENSITIVE 2 (KAI2) is the putative karrikin receptor identified in Arabidopsis. Here we show that B. tournefortii expresses three KAI2 homologues, and the most highly-expressed homologue is sufficient to confer enhanced responses to KAR relative to KAR when expressed in Arabidopsis. We identify two amino acid residues near the KAI2 active site that explain the ligand selectivity, and show that this combination has arisen independently multiple times within dicots. Our results suggest that duplication and diversification of KAI2 proteins could confer differential responses to chemical cues produced by environmental disturbance, including fire.
野火可以通过释放强效的萌发刺激剂（如卡瑞林）来促进入侵植物的建立。卡瑞林（KAR）是从燃烧的植被中产生的典型卡瑞林，它强烈刺激了地中海气候中有害杂草 Brassica tournefortii 的种子萌发。相比之下，密切相关但与火灾无关的短命拟南芥（Arabidopsis thaliana）则不同寻常，因为它更倾向于对 KAR 做出响应。α/β-水解酶 KARRIKIN INSENSITIVE 2（KAI2）是在拟南芥中鉴定出的假定卡瑞林受体。在这里，我们表明 B. tournefortii 表达了三个 KAI2 同源物，并且表达水平最高的同源物在拟南芥中相对于 KAR 赋予了增强的 KAR 响应。我们确定了 KAI2 活性位点附近的两个氨基酸残基，这些残基解释了配体的选择性，并表明这种组合在双子叶植物中已经独立地出现了多次。我们的研究结果表明，KAI2 蛋白的复制和多样化可能赋予了对环境干扰（包括火灾）产生的化学信号的不同响应。
