Unlike most animal tissue networks, the patterns of vein networks in plant leaves are variable and plastic, suggesting distinct control mechanisms. Thus, knowledge of the gene regulatory circuits that pattern leaf vein networks could suggest new control mechanisms of tissue network formation. However, the cis-regulatory elements required for expression at early stages of vein development are largely unknown. Here we show that the Arabidopsis genes CYCLIN A2;1 (CYCA2;1) and CYCLIN A2;4 (CYCA2;4), previously shown to act redundantly in vein cell proliferation, are expressed at early stages of vein development. We show that stage-specific expression of CYCA2;1 and CYCA2;4 in vein development depends on regulatory elements containing, respectively, one and three evolutionarily conserved transcription-factor binding sites. Our data suggest that early vein expression is encoded in regulatory elements of different structures.
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