Abstract
The highly conserved plant microRNA, miR156, is an essential regulator for plant development. In Arabidopsis (Arabidopsis thaliana), miR156 modulates phase changing through its temporal expression in the shoot. In contrast to the gradual decrease over time in the shoot (or whole plant), we found that the miR156 level in rice (Oryza sativa) gradually increased from young leaf to old leaf after the juvenile stage. However, the miR156-targeted rice SQUAMOSA-promoter binding-like (SPL) transcription factors were either dominantly expressed in young leaves or not changed over the time of leaf growth. A comparison of the transcriptomes of early-emerged old leaves and later-emerged young leaves from wild-type and miR156 overexpression (miR156-OE) rice lines found that expression levels of 3,008 genes were affected in miR156-OE leaves. Analysis of temporal expression changes of these genes suggested that miR156 regulates gene expression in a leaf age-dependent manner, and miR156-OE attenuated the temporal changes of 2,660 genes. Interestingly, seven conserved plant microRNAs also showed temporal changes from young to old leaves, and miR156-OE also attenuated the temporal changes of six microRNAs. Consistent with global gene expression changes, miR156-OE plants resulted in dramatic changes including precocious leaf maturation and rapid leaf/tiller initiation. Our results indicate that another gradient of miR156 is present over time, a gradual increase during leaf growth, in addition to the gradual decrease during shoot growth. Gradually increased miR156 expression in the leaf might be essential for regulating the temporal expression of genes involved in leaf development.
Highlights
The highly conserved plant microRNA, miR156, is an essential regulator for plant development
Global expression profiling analysis revealed that more than 3,000 genes were affected with altered expression levels in miR156 overexpression rice, and most of these genes were up-regulated in the old leaves. miR156 affected the temporal expression of several plant conserved microRNAs
We noticed that the miR156 level showed dramatic differences between old and young leaves, which prompted us to investigate the variation of miR156 expression level in the developing or growing leaves from a single plant
Summary
The highly conserved plant microRNA, miR156, is an essential regulator for plant development. MiR156 is dominantly expressed in juvenile shoot (or shoot apex) and decreased when the plant matures, and a low level of miR156 promotes adult phase development (Wu and Poethig, 2006; Chuck et al, 2007; Wu et al, 2009) This temporal expression pattern of miR156 is essential for its regulatory roles in phase change. We found that the miR156 level is increased gradually over time in developing adult leaves This is different from the reported temporal expression pattern in Arabidopsis, in which miR156 expression is gradually reduced in the shoots during plant growth. MiR156 affected the temporal expression of several plant conserved microRNAs. Our results imply that a gradual increase of miR156 expression may be essential for leaf development by attenuating temporal expression changes of the relevant genes
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