Restoration of DWF4 expression to the leaf margin of a dwf4 mutant is sufficient to restore leaf shape but not size: the role of the margin in leaf development

Abstract

The role of the margin in leaf development has been debated over a number of years. To investigate the molecular basis of events in the margin, we performed an enhancer trap screen to identify genes specifically expressed in this tissue. Analysis of one of these lines revealed abnormal differentiation in the margin, accompanied by an abnormal leaf size and shape. Further analysis revealed that this phenotype was due to insertion of the trap into DWF4, which encodes a key enzyme in brassinolide biosynthesis. Transcripts for this gene accumulated in a specific and dynamic pattern in the epidermis of young leaf primordia. Targeted expression of DWF4 to a subset of these cells (the leaf margin) in a dwf4 mutant background led to both restoration of differentiation of a specific group of leaf cells (margin cells) and restoration of wild-type leaf shape (but not leaf size). Ablation of these cells led to abrogation of leaf development and the formation of small round leaves. These data support the hypothesis that events in the margin play an essential role in leaf morphogenesis, and implicate brassinolide in the margin as a key mediator in the control of leaf shape, separable from a general function of this growth factor in the control of organ size.

Tyrosine phosphorylation of the BRI1 receptor kinase emerges as a component of brassinosteroid signaling in Arabidopsis

“…Important to the present study, however, is that two of the phenotypes associated with the BRI1(Y831F) mutant were restored to wild type by the acidic substitutions, which is consistent with a role for phosphotyrosine-831 in BR signaling in vivo. Although details remain unclear, our results are generally consistent with recent findings that BR signaling controls leaf size (28), leaf shape (29), and flowering (16). Molecular details of how Tyr-831 in its phosphorylated or dephosphorylated forms is involved in these processes remain to be elucidated, but our findings provide the foundation for further studies of tyrosine signaling involving BRI1 and other receptor kinases.…”

Targeted manipulation of leaf form via local growth repression

“…As our data indicate that the tools used to modify leaf shape act downstream of the patterning elements involved in leaf and vascular formation, they may provide a useful background to investigate the relationship between these elements (Dengler and Kang, 2001). Our data also indicate that growth events targeted to the margin can influence leaf shape, supporting the proposed importance of this region of the leaf in aspects of leaf morphogenesis (Reinhardt et al, 2007). As well as 2D shape, co-ordination of growth is necessary for appropriate 3D leaf architecture.…”

Steroids are required for epidermal cell fate establishment in Arabidopsis roots

“…Recent studies have demonstrated that BRs acting in the epidermis are essential for growth of aerial tissues (23,24). In this study, we show that BRs are required for normal expression and patterning of master regulators of epidermal cell fate.…”