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Dynamic growth re-orientation orchestrates flatness in the Arabidopsis leaf
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Abstract The growth and division of cells in plant leaves is highly dynamic in time and space, all while the cells cannot move relative to their neighbors. Given these constraints, models predict that long range regulatory systems must exist to maintain flat forms. Juxtaposed microRNA (miR-NA) networks could serve as one of these regulatory systems. One of these miRNAs, miR319 is thought to be expressed from the base of leaves and to promote growth by degrading class II TCP transcription factor mRNAs. A miR319 overexpression mutant, jagged and wavy ( jaw-D ) exhibits rippling and undulating leaves, consistent with biomechanical predictions that without genetic spatial coordination, tissues will deform. It has been theorized that jaw-D rippling results from overgrowth at the margins, however this does not fully address how miR319 expression from the base of wild-type (WT) leaves allows them to flatten. Here, we track the growth, cell division and cell maturation in live WT and jaw-D leaves to ask how miR319 expression in WT promotes flattening. This data revealed the importance of spatially distinct growth, division and differentiation patterns in WT leaves, which are missing in jaw-D. We propose that WT leaf cells respond to differentiation cues to dynamically re-orient growth in specific tissue locations and regulate flattening.
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