The role of class I TCP genes in determining leaf shape and size

Leaf shape is an important feature of plant development and is known to be controlled by genetic, hormonal and environmental factors. Leaves are the plants photosynthetic organs and provide the plant with the energy to grow. Leaf size and shape, and especially the alteration of leaf size and shape, in mutants can provide us with valuable insight into the genetic basis of leaf development. Alterations in the regulatory control of early leaf development can be visualised by analysing the mature leaf. However, the human eye is not made to identify subtle differences between shapes and we have therefore used automated quantitative imaging technology to quantify differences in shape. In this thesis we employ landmark-based geometric morphometrics to analyse Arabidopsis leaf size and shape. We have quantified the natural leaf size and shape variation in Arabidopsis and built a Leaf Size and Shape Library using Arabidopsis accessions.

The Arabidopsis leaf shape library has been applied to the leaf size and shape characterization of a sub-clade of plant specific class I TCP transcription factors (TCP8, TCP14, TCP15, TCP22 and TCP23) in an attempt to better understand their role in leaf development. Functional characterization of class I TCP genes has been hampered by a high degree of redundancy between its family members. We have discovered that TCP14 and TCP15 repress cell proliferation in leaves and thereby modulate leaf shape, combined with work from Kieffer et al., 2011 it constitutes proof that class I TCP genes can activate or repress transcription in a tissue dependent manner. TCP8, TCP22 and TCP23 have a yet to be determined role in modulating leaf shape that may work separately from TCP14/TCP15. TCP8 and TCP23 appear to have a regulatory role that is not limited to leaves.