The functional homologs WS1A and WS1B, identified by map-based cloning, control the burley character by affecting chloroplast development in tobacco, contributing to gene isolation and genetic improvement in polyploid crops. Burley represents a special type of tobacco (Nicotiana tabacum L.) cultivar that is characterized by a white stem with a high degree of chlorophyll deficiency. Although important progress in the research of burley tobacco has been made, the molecular mechanisms underlying this character remain unclear. Here, on the basis of our previous genetic analyses and preliminary mapping results, we isolated the White Stem 1A (WS1A) and WS1B genes using a map-based cloning approach. WS1A and WS1B are functional homologs with completely identical biological functions and highly similar expression patterns that control the burley character in tobacco. WS1A and WS1B are derived from Nicotiana sylvestris and Nicotiana tomentosiformis, the diploid ancestors of Nicotiana tabacum, respectively. The two genes encode zinc metalloproteases of the M50 family that are highly homologous to the Ethylene-dependent Gravitropism-deficient and Yellow-green 1 (EGY1) protein of Arabidopsis and the Lutescent 2 (L2) protein of tomato. Transmission electron microscopic examinations indicated that WS1A and WS1B are involved in the development of chloroplasts by controlling the formation of thylakoid membranes, very similar to that observed for EGY1 and L2. The genotyping of historical tobacco varieties revealed that a two-step mutation process occurred in WS1A and WS1B during the evolution of burley tobacco. We also discussed the strategy for gene map-based cloning in polyploid plants with complex genomes. This study will facilitate the identification of agronomically important genes in tobacco and other polyploid crops and provide insights into crop improvement via molecular approaches.

中文翻译：

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双 WS1 同源物的两步突变过程驱动白肋烟的进化，白肋烟是一种特殊的叶绿素缺陷突变体，叶绿体发育异常


通过图位克隆鉴定的功能同源物 WS1A 和 WS1B 通过影响烟草叶绿体发育来控制白肋烟特性，有助于多倍体作物的基因分离和遗传改良。白肋烟代表了一种特殊类型的烟草（Nicotiana tabacum L.）品种，其特征是白色茎，叶绿素高度缺乏。尽管白肋烟的研究已取得重要进展，但这一特性背后的分子机制仍不清楚。在这里，根据我们之前的遗传分析和初步图谱结果，我们使用基于图谱的克隆方法分离了White Stem 1A（WS1A）和WS1B基因。 WS1A和WS1B是功能同系物，具有完全相同的生物学功能和高度相似的控制烟草白肋烟特性的表达模式。 WS1A 和 WS1B 分别源自烟草 (Nicotiana sylvestris) 和毛毛烟草 (Nicotiana tomentosiformis)，它们是烟草 (Nicotiana tabacum) 的二倍体祖先。这两个基因编码 M50 家族的锌金属蛋白酶，与拟南芥的乙烯依赖性向地性缺陷型黄绿 1 (EGY1) 蛋白和番茄的 Lutescent 2 (L2) 蛋白高度同源。透射电子显微镜检查表明，WS1A 和 WS1B 通过控制类囊体膜的形成参与叶绿体的发育，与 EGY1 和 L2 观察到的情况非常相似。对历史烟草品种的基因分型表明，白肋烟进化过程中WS1A和WS1B发生了两步突变过程。我们还讨论了在具有复杂基因组的多倍体植物中基于基因图谱的克隆策略。 这项研究将有助于鉴定烟草和其他多倍体作物中重要的农艺基因，并通过分子方法提供对作物改良的见解。