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Abstract
Moderate curling generally causes upright leaf blades, which favors the establishment of ideal plant architecture and increases the photosynthetic efficiency of the population, both of which are desirable traits for super hybrid rice (Oryza sativa L.). In this study, we identified a novel curled-leaf mutant, curled flag leaf 2 (cfl2), which shows specific curling at the base of the flag leaf owing to abnormal epidermal development, caused by enlarged bulliform cells and increased number of papillae with the disordered distribution. Map-based cloning reveals that CFL2 encodes a cytochrome P450 protein and corresponds to the previously reported OsCYP96B4. CFL2 was expressed in all analyzed tissues with differential abundance and was downregulated in the clf1 mutant [a mutant harbors a mutation in the homeodomain leucine zipper IV (HD-ZIP IV) transcription factor Roc5]. Yeast one-hybrid and transient expression assays confirm that Roc5 could directly bind to the cis-element L1 box in the promoter of CFL2 before activating CFL2 expression. RNA sequencing reveals that genes associated with cellulose biosynthesis and cell wall-related processes were significantly upregulated in the cfl2 mutant. The components of cell wall, such as lignin, cellulose, and some kinds of monosaccharide, were altered dramatically in the cfl2 mutant when compared with wild-type “Jinhui10” (WT). Taken together, CFL2, as a target gene of Roc5, plays an important role in the regulation of flag leaf shape by influencing epidermis and cell wall development.
Highlights
The leaf is the primary photosynthesis organ in plants
No significant difference in plant height was observed between wild-type “Jinhui10” (WT) and the cfl2 mutant (Figure 1C and Supplementary Figure S1)
Both of the allelic mutants exhibited a dwarfism phenotype, which is different from the cfl2, their flag leaves were curly (Supplementary Figure S2)
Summary
The morphological characteristics of leaves, such as shape, size, and thickness, directly affect light utilization and influence the yield of crops (Zhang et al, 2015). Moderate curling is beneficial for the development of an erect leaf, which improves the population structure and increases the light utilization, and has important outcomes for breeding high-yield rice (Richards et al, 2002; Wang et al, 2020). The morphology, number, size, and distribution of the bulliform cells in the epidermis are the predominant factors that affect leaf rolling. Some genes related with secondary cell wall or cellulose formation, such as CELLULOSE SYNTHASELIKE D4 (OsCSLD4/NRL1) (Li et al, 2009; Hu et al, 2010; Luan et al, 2011), ROLLING LEAF14 (RL14) (Fang et al, 2012), and OsMYB103L (Yang et al, 2014), influence the bulliform cell development
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