由黄单胞杆菌水稻致病变种Xanthomonas oryzae pv. oryzae (Xoo)引起的白叶枯病是水稻重要细菌性病害之一。迄今，已有7个水稻白叶枯病抗性基因被克隆。Xa21是第一个被克隆的白叶枯病抗性基因，因具有广谱抗性而受到广泛的关注。对Xa21的发现、定位及克隆、表达特征、编码产物XA21的生化特性、作用与调控以及XA21介导的免疫反应模式等方面的研究结果进行综述，并对今后的研究方向进行展望。
The bacterial blight of rice caused by Xanthomonas oryzae pv. oryzae（Xoo）is one of the most destructive diseases in the world. Up to now, 7 bacterial blight resistance genes have been cloned. Xa21 is the first bacterial blight disease resistance gene cloned from rice and it has drawn great attention because of its broad spectrum resistance against Xoo. This paper briefly reviewed the discovery, mapping, cloning, expression properties of Xa21, biochemical properties, action and regulation of XA21 and XA21-mediated immunity. Future perspective on Xa21-related research were also discussed.