Abstract
Leaf size and flatness directly affect photosynthesis and are closely related to agricultural yield. The final leaf size and shape are coordinately determined by cell proliferation, differentiation, and expansion during leaf development. Lettuce (Lactuca sativa L.) is one of the most important leafy vegetables worldwide, and lettuce leaves vary in shape and size. However, the molecular mechanisms of leaf development in lettuce are largely unknown. In this study, we showed that the lettuce APETALA2 (LsAP2) gene regulates leaf morphology. LsAP2 encodes a transcriptional repressor that contains the conserved EAR motif, which mediates interactions with the TOPLESS/TOPLESS-RELATED (TPL/TPR) corepressors. Overexpression of LsAP2 led to small and crinkly leaves, and many bulges were seen on the surface of the leaf blade. LsAP2 physically interacted with the CINCINNATA (CIN)-like TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) transcription factors and inhibited their transcriptional activation activity. RNA sequencing analysis showed that LsAP2 affected the expression of auxin- and polarity-related genes. In addition, LsAP2 directly repressed the abaxial identity gene KANADI2 (LsKAN2). Together, these results indicate that LsAP2 regulates leaf morphology by inhibiting CIN-like TCP transcription factors and repressing LsKAN2, and our work provides insights into the regulatory mechanisms of leaf development in lettuce.
Highlights
Leaves are important plant organs in which photosynthesis converts carbon dioxide and water to carbohydrates and oxygen[1]
To determine the potential functions of LsAP2 during vegetative growth in lettuce, we explored its expression patterns in vegetative tissues by quantitative real-time PCR
Because the shoot apex supports the vertical growth of lettuce and gives rise to all other lateral meristems and organs[28], we investigated the expression of LsAP2 in shoot apexes at different vegetative growth stages
Summary
Leaves are important plant organs in which photosynthesis converts carbon dioxide and water to carbohydrates and oxygen[1]. Leaf size is crucial for photosynthesis because leaf area directly affects light absorption[2]. Most plants have evolved flat leaves to efficiently capture light energy[3]. Large and flat leaves photosynthesize strongly and synthesize more organic compounds than other leaf types[4]. Because leaf size and flatness are closely related to agricultural yield, understanding the regulatory mechanisms and genetic bases of leaf development will contribute to the improvement of crop production. Leaf development is initiated from the shoot apical meristem and is controlled by complex regulatory mechanisms[5]. Leaf primordia are specified in the flanking region of the shoot apical meristem. The leaves become fully developed, revealing their specific sizes and shapes[2,3]
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