Developmental genetics of allometric variation between species

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As living organisms grow, they also change shape. The human head, for instance, grows more slowly than the rest of the body, and so makes up less of the total size of an adult than a baby. Similar changes in shape and size have been important in the evolution of new species and are important in the breeding of crops and livestock (e.g. plants with bigger fruits). Although the importance of changes in both size and shape was recognised over 80 years ago, when the phenomenon was named allometry (from the Greek allo ` different¿ and metron `measure¿), its causes are still mostly unknown. We have used plant leaves and petals as examples of growing shapes to understand how allometry is controlled. We hybridised two snapdragon (Antirrhinum) species with different sized leaves and petals. By comparing the size of these organs in each of the offspring with the genes it had inherited, we were able to locate the genes responsible for differences in organ size. These genes also affected shape (i.e. controlled allometry). We will use this finding along with new techniques and plant varieties that we have developed, to make the first integrated study of the causes of natural variation in allometry. We will attempt to discover how leaves and petals change shape as they grow and how allometry genes affect these changes. This will involve approaches similar to medical CAT scanning and time-lapse photography to image growing organs. Because leaves and particularly petals are not completely flat, we will develop computer software to navigate and record 3D shapes from these images. We will also examine whether the same genes are responsible for differences in leaves and petals between other snapdragon species and how the genes act together to control the final shape and size of organs. Because a plant normally produces leaves with different shapes and sizes from the bottom of the stem to the top (a phenomenon known as heteroblasty), one intriguing question is whether heteroblasty and allometry are related (e.g. are they controlled by similar genes). Finally, we will try to identify the DNA sequences of at least two of the allometry genes. Later this will allow us to study how the proteins produced by these genes influence growth and to examine how mutations in the genes have allowed evolution of leaves and petals with different shapes and sizes. Joint with BB/D522089/1 and BB/D522438/1