The mechanisms underlying leafy heads in vegetables are poorly understood. Here, we cloned a quantitative trait locus (QTL) controlling leafy heads in lettuce (Lactuca sativa). The QTL encodes a transcription factor, SAWTOOTH 1 (LsSAW1), which has a BEL1-like homeodomain and is a homolog of Arabidopsis thaliana. A 1-bp deletion in Lssaw1 contributes to the development of leafy heads. Laser-capture microdissection and RNA-sequencing showed that LsSAW1 regulates leaf dorsiventrality and loss-of-function of Lssaw1 downregulates the expression of many adaxial genes but upregulates abaxial genes. LsSAW1 binds to the promoter region of the adaxial gene ASYMMETRIC LEAVES 1 (LsAS1) to upregulate its expression. Overexpression of LsAS1 compromised the effects of Lssaw1 on heading. LsSAW1 also binds to the promoter region of the abaxial gene YABBY 1 (LsYAB1), but downregulates its expression. Overexpression of LsYAB1 led to bending leaves in LsSAW1 genotypes. LsSAW1 directly interacts with KNOTTED 1 (LsKN1), which is necessary for leafy heads in lettuce. RNA-seq data showed that LsSAW1 and LsKN1 exert antagonistic effects on the expression of thousands of genes. LsSAW1 compromises the ability of LsKN1 to repress LsAS1. Our results suggest that downregulation or loss-of-function of adaxial genes and upregulation of abaxial genes allow for the development of leafy heads.

中文翻译：

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SAWTOOTH 1 功能丧失会影响叶背心基因，从而促进生菜的叶头生长。


人们对蔬菜叶状头的机制知之甚少。在这里，我们克隆了控制生菜（Lactuca sativa）叶头的数量性状基因座（QTL）。 QTL 编码转录因子 SAWTOOTH 1 (LsSAW1)，它具有类似 BEL1 的同源结构域，是拟南芥的同源物。 Lssaw1 中的 1-bp 缺失有助于叶状头的发育。激光捕获显微切割和 RNA 测序表明，LsSAW1 调节叶背心，Lssaw1 功能丧失会下调许多近轴基因的表达，但上调远轴基因的表达。 LsSAW1 与近轴基因 ASYMMETRIC LEAVES 1 (LsAS1) 的启动子区域结合，上调其表达。 LsAS1 的过度表达损害了 Lssaw1 对抽穗的影响。 LsSAW1 还与远轴基因 YABBY 1 (LsYAB1) 的启动子区域结合，但下调其表达。 LsYAB1 的过度表达导致 LsSAW1 基因型的叶片弯曲。 LsSAW1 直接与 KNOTTED 1 (LsKN1) 相互作用，这对于生菜的叶状头是必需的。 RNA-seq数据显示LsSAW1和LsKN1对数千个基因的表达产生拮抗作用。 LsSAW1 损害了 LsKN1 抑制 LsAS1 的能力。我们的结果表明，近轴基因的下调或功能丧失以及远轴基因的上调允许叶状头部的发育。