Genetic regulation of leaf shape and impacts on photosynthesis.

By 11/22/2023Current Projects
HSF 22022 | Amount: $58,500 | Project Leader: M Byrne | Project Period: 0

A project undertaken at The University of Sydney, and supervised by A/Prof Mary Byrne.

Leaves can be thought of as the engine room of plants. They are three dimensional structures within which cells carry out the critical function of photosynthesis. They are most often flat with a distinct top side that faces towards the sun and a bottom side that faces away from the sun.

A look inside the leaf reveals that the arrangement of cells on the top side is optimised to capture sunlight and cell arrangement on the bottom side is optimised for gas exchange. The top and bottom halves of the leaf therefore have a design that maximises light capture and conversion of sunlight into energy for plant growth. 

The top and bottom sides of a leaf are in fact critically important for development of a leaf; there is no flat leaf unless there is both a top and a bottom. But looking around our garden we can see that leaves are not just flat structures. They occur in vast variety of different shapes. Leaves on some plants are fairly simple, being round or oval in shape. Other plants have leaves that are lobed or divided into leaflets. All of these types of leaves may be modified further by small outgrowths or serrations along the leaf or leaflet edges, thus increasing the leaf shape complexity.

What determines the shape of leaves? It is actually the patten of growth at the edges of the developing leaf. For instance, serrations along the edge of the leaves in the model plant species Arabidopsis thaliana arise because some regions of the leaf edge are programmed to keep growing while adjacent regions are programmed to stop growing. Altering the timing and extent of the regions of growth and no growth results in different degrees of leaf margin elaboration.

We are using Arabidopsis thaliana to investigate a family of homeobox transcription factor genes that are involved in modifying the growth pattern at the edge of leaves. There is substantial redundancy within this gene family, but leaf shape changes occur when there are mutations in multiple genes. Surprisingly we have found that these genes are expressed on the top side of the leaf even though they function in growth at the leaf margin. We are using genetics to investigate the relationship of top-bottom to leaf margin growth.

Do changes in these genes contribute to more complex leaf shapes in other species? To answer this question, we are using gene editing as a tool to make mutations in these homeodomain transcription factor genes in the model plant species Cardamine hirsute, which has a compound leaf shape. Lastly, what is the significance of different leaf shapes? We are examining whether leaf shape affects photosynthesis, the output of the engine room, in different growth conditions. This work will help to explain the variation in plants that we see in Nature.