Lettuce (Lactuca sativa) is one of the most important vegetables worldwide and an ideal plant for producing protein drugs. Both well-functioning chloroplasts that perform robust photosynthesis and small leaf angles that enable dense planting are essential for high yields. In this study, we used an F₂ population derived from a cross between a lettuce cultivar with pale-green leaves and large leaf angles to a cultivar with dark-green leaves and small leaf angles to clone LsNRL4, which encodes an NPH3/RPT2-Like (NRL) protein. Unlike other NRL proteins in lettuce, the LsNRL4 lacks the BTB domain. Knockout mutants engineered using CRISPR/Cas9 and transgenic lines overexpressing LsNRL4 verified that LsNRL4 contributes to chloroplast development, photosynthesis and leaf angle. The LsNRL4 gene was not present in the parent with pale-green leaves and enlarged leaf angles. Loss of LsNRL4 results in the enlargement of chloroplasts, decreases in the amount of cellular space allocated to chloroplasts and defects in secondary cell wall biosynthesis in lamina joints. Overexpressing LsNRL4 significantly improved photosynthesis and decreased leaf angles. Indeed, the plant architecture of the overexpressing lines is ideal for dense planting. In summary, we identified a novel NRL gene that enhances photosynthesis and influences plant architecture. Our study provides new approaches for the breeding of lettuce that can be grown in dense planting in the open field or in modern plant factories. LsNRL4 homologues may also be used in other crops to increase photosynthesis and improve plant architecture.

中文翻译：

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LsNRL4 增强光合作用并降低生菜的叶角

莴苣（Lactuca sativa）是世界上最重要的蔬菜之一，是生产蛋白质药物的理想植物。执行强大光合作用的功能良好的叶绿体和能够密集种植的小叶角对于高产都是必不可少的。在这项研究中，我们使用了一个 F ₂群体，该群体来源于一个具有淡绿色叶子和大叶角的莴苣品种与一个具有深绿色叶子和小叶角的品种之间的杂交，以克隆LsNRL4，它编码 NPH3/RPT2-像（NRL）蛋白质。与生菜中的其他 NRL 蛋白不同，LsNRL4 缺少 BTB 结构域。使用 CRISPR/Cas9 设计的敲除突变体和过表达LsNRL4的转基因系证实了LsNRL4有助于叶绿体发育、光合作用和叶角。LsNRL4基因在叶片淡绿色和叶角增大的亲本中不存在。LsNRL4 的缺失导致叶绿体增大、分配给叶绿体的细胞空间量减少以及叶片关节中次生细胞壁生物合成的缺陷。过表达LsNRL4显着改善了光合作用并降低了叶角。事实上，过度表达系的植物结构非常适合密集种植。总之，我们发现了一种新的NRL增强光合作用并影响植物结构的基因。我们的研究为生菜的育种提供了新的方法，这些生菜可以在露天或现代植物工厂的密集种植中种植。LsNRL4同系物也可用于其他作物以增加光合作用和改善植物结构。