The Irish lab is interested in understanding the molecular mechanisms controlling 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 transgenic approaches to identify the genes and processes responsible for thorn development and how this unusual stem cell arrest process is controlled. We have developed a number of molecular tools for work with Citrus to facilitate this work. In collaboration with Yannick Jacob’s lab, we have developed CRISPR/Cas9 methods for inducing mutations in Citrus at a high rate. Economically, Citrus is the most important fruit crop in the US, and so our strategies to manipulate the Citrus genome are a valuable addition to the arsenal of tools to work with this genus. Since plant growth, fruit yield and harvest costs are all affected by thorniness, understanding how to manipulate thorn production will greatly impact the economics of this valuable crop.

supported by grant #5200-151 from the Citrus Research Board, and grant #1354389 from the National Science Foundation.

For more information see:

Rossignol, P., Orbović, V., Irish, V.F. 2014. A dexamethasone-inducible gene expression system is active in Citrus plants. Sci. Hort. 172, 47-53.

Zhang, F., LeBlanc, C., Irish, V.F., Jacob, Y. 2017. Rapid and efficient CRISPR/Cas9 gene editing in Citrus using the YAO promoter. Plant Cell Rep. in press.

Control of petal growth

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 we have shown 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.

supported by grant #1615387 from the National Science Foundation

For more information see:

Huang, T., Lopez-Giraldez, F., Townsend, J.P., and Irish, V.F. 2012. RBE controls microRNA164 expression to effect floral organogenesis. Development 139: 2161-2169.

Huang, T. and Irish, V.F. 2015. Temporal control of plant organ growth by TCP transcription factors. Current Biology 25: 1765-1770.

Huang, T. and Irish, V.F. 2016. Gene networks controlling petal organogenesis. J. Exp. Bot. 67:61-8.

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.

supported by grant #1615387 from the National Science Foundation

For more information see:

Irish, V.F. 2008. The Arabidopsis petal: a model for plant organogenesis. Trends Plant Sci 13:430-436.

Saffer, A.M., Carpita, N.C. and Irish, V.F. 2017. Rhamnose-containing cell wall polymers suppress helical plant growth independently of microtubule orientation. Current Biology 27:2248-2259.