Our lab is interested in pattern formation during plant development. The Arabidopsis petal is an ideal system for these studies, since it is dispensable for growth and reproduction, has a simple laminar structure, and is composed of only a few cell types. Using forward and reverse genetic approaches, as well as biochemical and genomic strategies, we are characterizing the transcriptional networks responsible for different aspects of petal development. We have also examined how cell-cell interactions regulate petal patterning. In order to understand how the developmental mechanisms responsible for floral patterning have evolved to give rise to the diversity of floral forms that we see today, we are characterizing these pathways in several other species. Using these approaches, we hope to elucidate how dividing cells acquire information about their position and differentiate accordingly, as well as how these processes have been modulated through evolution.
Extensive Research Description
The Irish lab is interested in understanding plant growth and development. Our current research efforts are described below.
Stem cell proliferation and arrest in Citrus
In plants, cells of the shoot apical meristem (SAM) act as stem cells, giving rise to more stem cells as well as specialized cell types contributing to the leaves, branches and fruit. We are investigating the basis for thorn development in Citrus as a means to understand how the termination of stem cell proliferation is controlled. Thorns arise from SAM cells that fail to self-renew, and instead terminally differentiate, providing a unique opportunity to explore how SAM cell proliferation is controlled. We are using a combination of transcriptomics, molecular genetics and newly developed transgenic approaches to identify the genes and processes responsible for thorn development and how this unusual stem cell arrest process is controlled. Citrus plant growth, fruit yield and harvest costs are all affected by thorniness, and so understanding how to manipulate thorn production will also greatly impact the economics of this valuable fruit crop.
Control of petal organogenesis
Organ formation, whether in animals or plants, depends on several processes. These include delimitation of where an organ will form, growth of the organ, and its consequent differentiation. Using the Arabidopsis petal as a model organ system, we are investigating the genes and cellular processes that contribute to the development of this seemingly simple organ type. We are examining how a transcriptional repressor, RBE, coordinately regulates both organ boundary formation and organ growth. We have shown that RBE acts early in petal development to control the formation of organ boundaries, and recent results suggest that RBE also regulates a transcriptional cascade of events that act as a timing mechanism to control organ growth. We are currently investigating the cellular basis for growth control in petals, and how transcriptional changes are manifested as changes in cell proliferation.
Control of petal cell type differentiation
Petal conical epidermal cells are covered in radiate nanoridges that give these cells unique physical properties. The nanoridges are vital for pollinator attraction, iridescence, wettability, and can provide tactile cues. However, the molecular, cellular, and mechanical bases for how this unusual cell type is formed and functions is not well understood. We are using a combination of biochemical, molecular genetic, and modeling approaches to develop a mechanistic understanding of how conical epidermal cell morphology is achieved.
- Abraham MC, Metheetrairut C, Irish VF. 2013. Natural variation identifies multiple loci controlling petal shape and size in Arabidopsis thaliana. PLoS One. 8:e56743
- Huang T, López-Giráldez F, Townsend JP, Irish VF. 2012. RBE controls microRNA164 expression to effect floral organogenesis. Development. 139:2161-9.
- Irish VF. 2010. The flowering of Arabidopsis flower development. Plant Journal 61: 1014-1028
- Mara CD, Huang T, Irish VF. 2010. The Arabidopsis floral homeotic proteins APETALA3 and PISTILLATA negatively regulate the BANQUO genes implicated in light signaling. The Plant Cell 22: 690-702.
- Chae E, Tan Q. K-G, Hill TA, Irish VF. 2008. An Arabidopsis F-box protein acts as a transcriptional cofactor to regulate floral development. Development 135: 1235-1245
- DeMartino G, Pan I, Emmanuel E, Levy AA, Irish VF. 2006. Functional analyses of two tomato APETALA3 genes demonstrate diversification in their roles in regulating flowering. The Plant Cell 18: 1833-1845.
- Lamb RS. Irish VF. 2003. Functional divergence within the APETALA3/ PISTILLATA floral homeotic gene lineages. Proc. Nat. Acad. Sci. 100: 6558-6563.
- Kramer, E.M. and V.F. Irish. 1999. Evolution of genetic mechanisms controlling petal development. Nature, 399: 144-148.