Genetics and evolution of leaf development

Gene Expression

We observed UNIFOLIATA gene expression in pea leaves using RNA in situ hybridisation and we saw that it was present in pea leaves as they developed (Figure 6).

 

Figure 6. Longitudinal section through a wild-type pea shoot showing UNIFOLIATA gene expression (dark purple colour) in developing leaves. Leaves initiate on alternate sides of the shoot apex (A) and elongate as they become older (P1 – P5). The first pair of leaflets is initiated at P2 (leaflets not visible in this section). Additional pairs of leaflets and tendrils are initiated later in development (P3 – P5).

 

 

 

There are many pea mutants available with alterations in their leaf architecture. Some have very complex leaves, such as the afila mutant (see Figure 7). When we looked at UNIFOLIATA gene expression in these altered leaves, we noticed that the more complex the leaf architecture, the longer UNIFOLIATA gene expression persisted (Gourlay et al., 2000, Plant Cell 12: 1279-1294).

Figure 7. UNIFOLIATA gene expression in developing pea leaves with three different architectures; wild-type (top), afila mutant (middle) and cochleata mutant (bottom).

Leaf architecture is shown on the black panels (left) and UNIFOLIATA gene expression, detected by RNA in situ hybridisation, is shown in the yellow panels (right). These are transverse sections across the shoot tip with the shoot apex seen as a circular shape in the centre of each picture. Stipules are seen as long, thin, vertically aligned shapes, rachides are seen as small circular shapes.

UNIFOLIATA is expressed in the growing rachis of a wild-type leaf (arrow, top).

Leaf architecture is altered in the afila mutant such that lateral rachides develop in place of leaflets. UNIFOLIATA is expressed in the central and lateral rachides of the afila mutant (arrows, middle). N.B. It is not expressed in the stipules of these leaves.

Leaf architecture is altered in the cochleata mutant such that lateral rachides develop in place of stipules. UNIFOLIATA is expressed in these developing rachides (arrow, bottom).

Because pinnate rachides express UNIFOLIATA and the unifoliata mutant fails to develop a pinnate leaf, we concluded that UNIFOLIATA is required for pinnate leaf architecture in peas.



Papers from our lab are highlighted in yellow.


 

 

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