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.
Combatting HLB with Gene Editing
The U.S. citrus industry is facing unprecedented challenges from the spread of citrus greening disease (i.e Huanglongbing or HLB) in citrus-growing states like Florida, Texas and California. While traditional breeding approaches using natural variation are one way of introducing HLB tolerance into select cultivars, alternative approaches to rapidly generate new cultivars that are resistant/tolerant to the HLB-causing bacterial pathogen would be extremely valuable. The overall goal of this two year USDA-supported project is to utilize the extensive transcriptomic and proteomic information available for HLB infected citrus to develop a large-scale population of CRISPR/Cas9 gene-edited citrus plants that can be screened for tolerance to HLB. This project will provide a sustainable resource (i.e. collection of citrus mutants) for the citrus research community that can also be screened for resistance to other diseases and for other value-added traits in the future, and thus accelerate discoveries that would benefit the U.S. citrus industry many years after the funding period is completed. As part of this project, we also propose to study the economic and societal impact of using gene-editing technologies like CRISPR/Cas9 to create new citrus cultivars, with a focus on increasing acceptance of gene-edited crops by consumers and growers. In the longer term, the mutations identified as enhancing defense against HLB can then be engineered into other commercially important citrus cultivars and field-tested in Florida and California. See our project website for more information: https://crisprcitrus.org/
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, how transcriptional changes are manifested as changes in cell proliferation, and the role of epigenetic mechanisms in controlling petal development.
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 have identified a new role for plant pectins in the control of conical cell shape and patterning. We are continuing to explore these processes using a combination of biochemical, molecular genetic, and modeling approaches to develop a mechanistic understanding of how conical epidermal cell morphology is achieved.
Improving Drought Tolerance in Plants Through Gene Editing
New gene editing technology has catalyzed the ability to improve global food production via the engineering of crops that can be more productive, more resilient to climate change, and require fewer resources by harnessing and manipulating their photosynthetic potential. In collaboration with Erika Edwards (Yale, Ecology and Evolutionary Biology) and her group, we aim to understand the functional significance of the dual photosynthetic mechanisms, C4 and crassulacean acid metabolism (CAM), operating in purslane, Portulaca amilis. By disrupting CAM photosynthesis using CRISPR/Cas9 approaches, we will be able to test the hypothesis that this mechanism produces high drought tolerance. This work exemplifies a new approach in testing hypotheses of evolutionary adaptation and take the first essential step toward engineering a CAM cycle into C4 crop species such as corn or sugarcane, resulting in more drought-resistant plants.
Our work is supported by grants from the National Science Foundation, the National Institutes of Health, the U.S. Department of Agriculture, the Citrus Research Board and the Yale Planetary Solutions Project.