<div><p>Proper leaf development is essential for plant growth and development, and leaf morphogenesis is under the control of intricate networks of genetic and environmental cues. We are interested in dissecting these regulatory circuits genetically and report here the isolation of two Arabidopsis dominant mutants, <i>abnormal shoot5-1D</i> (<i>abs5-1D</i>) and <i>abs7-1D</i> identified through activation tagging screens. Both <i>abs5-1D</i> and <i>abs7-1D</i> display an intriguing upwardly curly leaf phenotype. Molecular cloning showed that the elevated expression of a bHLH transcription factor ABS5/T5L1/bHLH30 or a MYB transcription factor ABS7/MYB101 is the cause for the abnormal leaf phenotypes found in <i>abs5-1D</i> or <i>abs7-1D</i>, respectively. Protoplast transient expression assays confirmed that both ABS5/T5L1 and ABS7/MYB101 are targeted to the nucleus. Interestingly, the expression domains of auxin response reporter <i>DR5::GUS</i> were abnormal in leaves of <i>abs5-1D</i> and <i>ABS5</i>/<i>T5L1</i> over-expression lines. Moreover, cotyledon venation analysis showed that more areoles and free-ending veins are formed in <i>abs5-1D</i>. We found that the epidermis-specific expressions of <i>ABS5</i>/<i>T5L1</i> or <i>ABS7</i>/<i>MYB101</i> driven by the Arabidopsis <i>Meristem Layer 1</i> promoter (<i>P<sub>AtML1</sub></i>) were sufficient to recapitulate the curly leaf phenotype of <i>abs5-1D</i> or <i>abs7-1D</i>. In addition, <i>P<sub>AtML1</sub>::ABS5</i> lines exhibited similar changes in <i>DR5::GUS</i> expression patterns as those found in 35S-driven <i>ABS5</i>/<i>T5L1</i> over-expression lines. Our work demonstrated that enhanced expressions of two transcription factors, ABS5/T5L1 and ABS7/MYB101, are able to alter leaf lamina development and reinforce the notion that leaf epidermis plays critical roles in regulating plant organ morphogenesis.</p></div