A novel transcriptional pathway that controls axillary meristem induction in grasses

Wheat is an agronomically important food crop worldwide that has evolved through a series of human-driven breeding events over the last ca.10,000 years. Because of this, most modern wheat varieties contain limited genetic variation, commonly referred to as 'genetic bottlenecks'. A trade-off of domestication or repetitive artificial selection was the reduction of secondary shoot outgrowth (branching), resulting in reduced tiller formation in most domesticated wheats compared with their highly-branched wild relatives. Since grains are produced from the tillers, increased tillering is now becoming a sought-after desirable trait to engineer in modern cultivars as it is one way to increase grain yield per hectare. Therefore, understanding how tiller formation occurs is important to ensure greater productivity of our modern food crops. By studying goat grass, a wild wheat relative which produces large albeit variable numbers of tillers per plant, we recently discovered a new molecular pathway that controls secondary branching and thus tiller number, which we named High Tiller Number 1 (HTN1). We also obtained exciting results demonstrating that induction of this pathway is sufficient to increase tiller numbers in modern wheat and rice varieties, suggesting functional conservation of this pathway in the grasses. Based on these exciting new findings, this project aims to elucidate the HTN1 pathway primarily in wheat, for which we have ample experience and unique genomic and genetic resources in hand. Specifically, we will use computational, developmental genetic and molecular approaches to unravel the exact nature of this pathway and uncover the various components and regulatory factors involved, including how the environment (e.g. temperature, nutrient availability) affects the HTN1 pathway.
We anticipate that this work will not only help us understand how tiller formation is achieved in wheat but will also provide essential know-how to protect and enhance yield in cereal crops.

Plant architecture is critical for reproductive success and thus has been subject to strong domestication selection in cereal crops over Millenia. Plant architecture is determined post-embryonically and underpinned by the activity of pluripotent stem cells present in meristems, such as the shoot apical and axillary meristems (AM). The production of tillers, or secondary shoots, by AM varies widely between the grasses, and impacts on yield; most domesticated species having significantly reduced or eliminated AM growth altogether compared to their wild relatives. To date, the mechanisms underlying AM initiation and regulation in grasses remain elusive despite being an important agronomical question; this knowledge could unlock greater yield potential in domesticated crops.
Our recent work in goat grass, a diploid wild wheat relative, has uncovered a new transcriptional pathway (High Tiller Number 1, HTN1) that is sufficient to induce axillary meristem formation in bread wheat, rice and likely other grasses. Based on these exciting findings, we propose to use wheat as our model system for which we have ample experience and unique genetic resources to:
1. Fully elucidate the HTN1 pathway is (by identifying upstream components and key regulatory factors). For this we will take a range of computational, transcriptomic, and molecular genetic approaches to identify and functionally characterise components of this pathway.
2. Understand how this pathway is activated and regulated in axils to direct changes in the above-ground architecture of agronomically important cereals to enhance or maintain their yield. For this, we will use epigenetic and state-of-the-art phenomics approaches to investigate the HTN1 pathway under different growth conditions.
Collectively, this work will provide fundamental understanding of how plant architecture is regulated and can be manipulated to create novel strategies and tools to protect and enhance yield in agronomically important cereals.