About

Robert Turgeon is a professor in the School of Integrative Plant Science, Plant Biology Section at Cornell University. His research focuses on the cell biology and physiology of phloem transport, with particular interest in leaf development, the structure and function of plasmodesmata, and virus movement. His work employs molecular, physiological, and anatomical techniques to study phloem loading, which involves the active accumulation of sugars in minor vein sieve elements and companion cells. Turgeon is known for his contribution to the 'polymer trap' model that explains phloem loading through plasmodesmata, challenging previous thermodynamic assumptions. His research also investigates the transport mechanisms of primary photosynthesis products, such as diffusion in certain plants like willow and apple, and explores how these mechanisms may serve to transport protective secondary metabolites. Additionally, Turgeon has developed experimental systems, such as transforming Verbascum phoeniceum, to test and refine models of phloem loading and transport, and collaborates on studies related to virus systemic transport and carbohydrate signaling. His work has advanced understanding of plant nutrient distribution, phloem structure, and the evolutionary aspects of phloem loading mechanisms.

Research topics

• Botany
• Biology
• Cell biology
• Biophysics
• Chemistry

Selected publications

• The Crucial Roles of Phloem Companion Cells in Response to Phosphorus Deficiency

  Plant Cell & Environment · 2025-02-17 · 2 citations

  articleOpen access

  Mineral deficiency is a major problem in agriculture. Plant adaption to low mineral environments involves signaling between shoots and roots, via the food transport cells, the sieve elements. However, due to the sequestered position of the sieve elements in the vascular bundles, identifying shoot-to-root mobile signals is challenging. In herbaceous species, sieve elements and companion cells (CCs) are isolated from other leaf tissues. We hypothesize that phloem CCs play an essential role by synthesizing shoot-to-root signals in response to mineral deficiency. To test this hypothesis, we analyzed gene expression responses in Arabidopsis CCs under phosphorus deficiency using TRAP-Seq. Phosphorus was chosen for its importance in plant growth and the known role of shoot-to-root signaling in regulating root phosphate transporters during deficiency. Our findings revealed that CCs exhibit more dramatic molecular responses than other leaf cells. We also found that many genes altered in CCs have potential functions in regulating root growth. This is unexpected because it has been widely believed that shoot-to-root signaling is not involved in root growth regulation under P deficiency. The importance of CCs in regulating mineral deficiency may extend beyond phosphorus because shoot-to-root signaling is a common response to the deficiency of various minerals.

  PublisherOA PDFDOI

• <i>Candidatus</i> Liberibacter asiaticus reduces callose and reactive oxygen species production in the phloem

  bioRxiv (Cold Spring Harbor Laboratory) · 2022-03-12 · 3 citations

  preprintOpen access

  Abstract Huanglongbing (HLB) causes significant economic loss in citrus production worldwide. HLB is caused by Candidatus Liberibacter asiaticus ( C Las), a gram-negative bacterium which inhabits the phloem exclusively. C Las infection results in accumulation of callose and reactive oxygen species in the phloem of infected plants, but little is known about the specific processes that take place during infection because of the sparse distribution of bacteria and the inaccessibility of the phloem inside the tree. In this study, we used the seed vasculatures, which accumulate a high number of C Las, as a model tissue to study C Las-host cellular interactions. In vasculature where C Las is abundant, sieve pore callose and H 2 O 2 concentration were reduced compared to healthy seed vasculature. The expression of callose synthases ( CalS ) and respiratory burst oxidase homolog ( RBOH ) genes were downregulated in infected seeds compared to healthy ones. In leaves of HLB-infected plants, H 2 O 2 concentration and CalS expression increased compared to uninfected leaves, but cells with C Las had lower levels of sieve plate callose compared to cells without C Las. Our results provide evidence that the bacteria manipulate cell metabolism to disable plant defenses and suggests that HLB disease is the result of a constant arms-race between the pathogen and a defense response, which is ultimately harmful to the host plant.

  PublisherOA PDFDOI

• <i>Candidatus</i> Liberibacter asiaticus accumulation in the phloem inhibits callose and reactive oxygen species

  PLANT PHYSIOLOGY · 2022 · 20 citations

  • Botany
  • Biology
  • Chemistry

  CLas inhibits callose deposition in the sieve pores and the accumulation of reactive oxygen species to favor its cell-to-cell movement.

  PublisherOA PDFDOI

• The Phloem as an Arena for Plant Pathogens

  Annual Review of Phytopathology · 2022 · 43 citations

  Senior authorCorresponding
  • Biology
  • Botany

  Liberibacter spp. are devastating citrus in many parts of the world. Given that most phloem pathogens are vectored, they are not exposed to applied chemicals and are therefore difficult to control. Furthermore, pathogens use the phloem network to escape mounted defenses. Our review summarizes the current knowledge of phloem anatomy, physiology, and biochemistry relevant to phloem/pathogen interactions. We focus on aspects of anatomy specific to pathogen movement, including sieve plate structure and phloem-specific proteins. Phloem sampling techniques are discussed. Finally, pathogens that cause particular harm to the phloem of crop species are considered in detail.

  PublisherDOI

• Complexity untwined: The structure and function of cucumber ( <i>Cucumis sativ</i> <i>us</i> L.) shoot phloem

  The Plant Journal · 2021 · 13 citations

  Senior authorCorresponding
  • Biology
  • Cell biology
  • Botany

  C as mobile tracers. We also mapped vascular architecture by conventional microscopy and X-ray computed tomography using optimized whole-tissue staining procedures. Differential gene expression in the internal (IP) and external phloem (EP) was analyzed by laser-capture microdissection followed by RNA-sequencing. The vascular bundles of the lamina form a nexus at the petiole junction, emerging in a predictable pattern, each bundle conducting photoassimilate from a specific region of the blade. The vascular bundles of the stem interconnect at the node, facilitating lateral transport around the stem. Elements of the extrafascicular phloem traverse the stem and petiole obliquely, joining the IP and EP of adjacent bundles. Using pairwise comparisons and weighted gene coexpression network analysis, we found differences in gene expression patterns between the petiole and stem and between IP and EP, and we identified hub genes of tissue-specific modules. Genes related to transport were expressed primarily in the EP while those involved in cell differentiation and development as well as amino acid transport and metabolism were expressed mainly in the IP.

  PublisherOA PDFDOI

• Physiological and Proteomic Responses of Mulberry Trees (Morus alba. L.) to Combined Salt and Drought Stress

  International Journal of Molecular Sciences · 2019-05-20 · 76 citations

  articleOpen access

  Intensive investigations have been conducted on the effect of sole drought or salinity stress on the growth of plants. However, there is relatively little knowledge on how plants, particularly woody species, respond to a combination of these two stresses although these stresses can simultaneously occur in the field. In this study, mulberry, an economically important resource for traditional medicine, and the sole food of domesticated silkworms was subjected to a combination of salt and drought stress and analyzed by physiological methods and TMT-based proteomics. Stressed mulberry exhibited significant alteration in physiological parameters, including root/shoot ratio, chlorophyll fluorescence, total carbon, and ion reallocation. A total of 577 and 270 differentially expressed proteins (DEPs) were identified from the stressed leaves and roots, respectively. Through KEGG analysis, these DEPs were assigned to multiple pathways, including carbon metabolism, photosynthesis, redox, secondary metabolism, and hormone metabolism. Among these pathways, the sucrose related metabolic pathway was distinctly enriched in both stressed leaves and roots, indicating an important contribution in mulberry under stress condition. The results provide a comprehensive understanding of the adaptive mechanism of mulberry in response to salt and drought stress, which will facilitate further studies on innovations in terms of crop performance.

  PublisherOA PDFDOI

• Mechanisms of phloem loading

  Current Opinion in Plant Biology · 2018-02-12 · 120 citations

  reviewSenior authorCorresponding
  PublisherDOI

• Transcriptomic and functional analysis of cucumber (<i>Cucumis sativus</i> L.) fruit phloem during early development

  The Plant Journal · 2018-09-08 · 53 citations

  articleOpen accessCorresponding

  Summary The phloem of the Cucurbitaceae has long been a subject of interest due to its complex nature and the economic importance of the family. As in a limited number of other families, cucurbit phloem is bicollateral, i.e. with sieve tubes on both sides of the xylem. To date little is known about the specialized functions of the internal phloem (IP) and external phloem (EP). Here, a combination of microscopy, fluorescent dye transport analysis, micro‐computed tomography, laser capture microdissection and RNA‐sequencing (RNA‐Seq) were used to study the functions of IP and EP in the vascular bundles (VBs) of cucumber fruit. There is one type of VB in the peduncle, but four in the fruit: peripheral (PeVB), main (MVB), carpel (CVB) and placental (PlVB). The VBs are bicollateral, except for the CVB and PlVB. Phloem mobile tracers and 14 C applied to leaves are transported primarily in the EP, and to a lesser extent in the IP. RNA‐Seq data indicate preferential gene transcription in the IP related to differentiation/development, hormone transport, RNA or protein modification/processing/transport, and nitrogen compound metabolism and transport. The EP preferentially expresses genes for stimulus/stress, defense, ion transport and secondary metabolite biosynthesis. The MVB phloem is preferentially involved in photoassimilate transport, unloading and long‐distance signaling, while the PeVB plays a more substantial role in morphogenesis and/or development and defense response. CVB and PlVB transcripts are biased toward development of reproductive organs. These findings provide an integrated view of the differentiated structure and function of the vascular tissue in cucumber fruit.

  PublisherDOI

• Export of Photosynthates from the Leaf

  Advances in photosynthesis and respiration · 2018-01-01 · 13 citations

  book-chapterSenior authorCorresponding
  PublisherDOI

• <i>FLOWERING LOCUS T</i> mRNA is synthesized in specialized companion cells in <i>Arabidopsis</i> and Maryland Mammoth tobacco leaf veins

  Proceedings of the National Academy of Sciences · 2018-02-26 · 125 citations

  articleOpen accessSenior author

  Significance Flowering in many plants begins with the perception of daylength in leaves. For example, some plants flower in short days, others in long days. In Arabidopsis thaliana , the leaves then transmit a small protein, FLOWERING TIME T (FT), to the shoot apex in the food-conducting cells, the phloem. Arrival of FT causes the apex to transition from leaf to flower formation. In this paper, we show that only two files of phloem cells in A. thaliana veins synthesize FT. This is also true for the Maryland Mammoth cultivar of tobacco ( Nicotiana tabacum ). Killing the cells specifically affects downstream, but not upstream, genes, indicating that an extensive intercellular signaling system regulates FT synthesis in the phloem.

  PublisherOA PDFDOI

Recent grants

• Heterogeneity in the phloem of minor veins

  NSF · $637k · 2014–2019

• Phloem Transport Without Phloem Loading

  NSF · $215k · 1997–2001

• A New Approach to the Study of Symplastic Phloem Loading

  NSF · $512k · 2005–2009

• Passive Phloem Loading

  NSF · $405k · 2012–2015

Frequent coauthors

• Brian G. Ayre

  University of North Texas

  22 shared

• Cankui Zhang

  Purdue University West Lafayette

  19 shared

• Véronique Amiard

  Agriaquaculture Nutritional Genomic Center

  16 shared

• Lailiang Cheng

  Cornell University

  15 shared

• Edwin J. Reidel

  Cornell University

  13 shared

• Emilie A. Rennie

  Lawrence Berkeley National Laboratory

  11 shared

• Richard Medville

  Electron Optica (United States)

  9 shared

• Xiyan Yu

  Zhejiang Chinese Medical University

  9 shared

Education

• PhD, Biology

  Carleton University

  1973

Awards & honors

• Charles Reid Barnes Lifetime Achievement Award 2013