Investigating the mechanisms of novel barley lemma shape development in Calcaroides-C

Abstract

The shape of plants is influenced by the complex interactions of gene expression, hormonal responses, and tissue patterning. The delineation of plant tissues into abaxial-adaxial (lower-upper), medio-lateral (centre to margin), and basal-apical (bottom to tip) domains, along with growth orientations, is crucial in shaping complex organs. Plant shape is a key component of plant productivity and in the case of crops, of potential yield. Understanding how shape is determined is important for advancing our understanding of the world around us and for potential crop improvement. One approach to studying plant shape determination is to examine developmental mutants, which can be leveraged to identify genes influencing plant shape.

Barley is a key cereal crop and is a model species for the study of developmental genetics. The barley lemma has a distal bristle-like extension called the awn which is important for grain development and has an interesting collection of shape mutants. The dominant Calcaroides-C (Cal-C) mutant has ectopic development of a sac and wing-like structures at the lemma-awn boundary. While previous research has mapped Cal-C to chromosome 5H, the Cal-C causal mutation and its influence on developmental pathways remains unclear. My thesis seeks to identify the Cal- C causal mutation and elucidate the mechanisms by which the Cal-C phenotype develops. To achieve this, I characterised the whole plant phenotype, effect on grain, cellular behaviour and transcriptomic changes. My research found that the Cal-C phenotype is specific to reproductive development. Analysis of lemma development found key differences in epidermal cell behaviour that may underlie the gross morphology previously reported. I found that the Cal-C lemma has ectopic expression of genes such as KNOX8 and KANADI1, both genes associated with patterning across axes.

My research into Cal-C provides insights into the mechanisms of novel shape determination in the barley lemma. In particular this work contributes further evidence that patterning genes can be redeployed in new contexts to generate novel 3D shape changes in plants.