From Rice Genomes to Single-Cell Metabolic Maps: C. Robin Buell Pioneers Crop Genomics
Background
Modern crop breeding no longer stops at reading DNA sequences but has advanced to interpreting gene function and expression locations to identify useful traits. However, in the early 2000s, assembling and annotating large plant genomes remained a technical challenge due to high repeat content, complex ploidy, and frequent chromosomal mixing among different lineages. At that time, researchers struggled to determine which genomic regions corresponded to genes and what roles these genes played in yield, disease resistance, and metabolism.
C. Robin Buell, a professor at the University of Georgia, as highlighted in PNAS, has been a leading plant genomicist working to bridge this gap since the dawn of DNA sequencing technology. She joined the Genome Institute in 1999 and led efforts in plant genome assembly, gene annotation, and comparative genomics. Her work has extended beyond staple crops like rice and potato to include plants such as Arabidopsis, maize, switchgrass, sweet potato, mint, and medicinal plants. In 2025, she was elected to the U.S. National Academy of Sciences for her contributions to plant genomic biology. According to the PNAS paper and NAS profile, this article is not a report of new experimental results but a profile summarizing her research trajectory and recent achievements.
Key Discoveries
Buell's early contributions transformed crop genomes into practical resources for researchers. She was a key member of the team that published the reference rice genome in 2005 and has maintained the rice genome annotation database for over two decades. In 2011, she also participated in the international potato genome sequencing consortium. By linking genomic assemblies with gene structure, protein function, and expression and co-expression data, she laid the foundation for identifying candidate genes for breeding.
Recent research has shifted focus to rare cell types hidden within tissue averages. In the Madagascar periwinkle, which produces the anticancer compounds vinblastine and vincristine, the biosynthetic pathway is distributed across three distinct cell types. Buell's team combined chromosome-level genome and single-cell transcriptome analyses to reveal that the 38-step monoterpene indole alkaloid pathway is sequentially localized in phloem-associated parenchyma, epidermal, and idioblast cells. Analyzing whole tissues often averages out signals from rare idioblast cells, making it easy to miss candidate genes, but single-cell expression maps clearly reveal the spatial division of labor.
In a follow-up study analyzing 11,321 stem cells from the tree Catharanthus roseus, the team identified 29,002 expressed genes and 23 cell clusters. Early iridoid synthase gene clusters were found concentrated in a cell population representing only 0.68% of the total plastid content. The researchers also identified MYB and bHLH transcription factors co-expressed in the same cells and proposed that the divergent transcription factor lineages used by C. roseus and the closely related Rauvolfia species reflect their evolutionary split approximately 115 million years ago.
Significance and Outlook
Buell's research encapsulates the trajectory of plant genomics. Starting from the early stage of reading reference genomes and annotating genes, the field has now advanced to tracking gene activation and metabolite movement within specific cell types. This approach can be applied not only to agricultural traits like yield and disease resistance but also to the design of plants for pharmaceuticals, biofuels, and biomaterials.
However, genome maps alone cannot establish causal relationships for traits. Candidate genes identified in single-cell transcriptomes must be validated through gene editing, overexpression, metabolite profiling, and field trials. There is also the possibility of cell loss or stress responses during plastid isolation. Future challenges include integrating pan-genomes, spatial transcriptomes, and single-cell metabolomes to reflect structural variations and complex ploidy across varieties. Long-term maintenance and standardization of public databases will also be critical for reproducibility and breeding utility.
Proceedings of the National Academy of Sciences, Volume 123, Issue 35, September 2026. C. Robin Buell has been a leading figure in plant genomics since the advent of DNA sequencing technology. She helped lead multiple consortia to sequence some of the first crop genomes at the turn of the millennium. She has since used the genomes to tackle ...
In breeding programs, candidate genes associated with disease resistance or tuber formation can be selected from rice and potato genome databases, followed by validation in gene-edited lines and diverse cultivation environments. Narrowing the search reduces the need for random screening of large breeding populations.
In the pharmaceutical and biotech industries, metabolic pathway maps of rare cells are valuable. For example, identifying transcription factors that regulate alkaloid synthesis in Madagascar periwinkle could enable their transfer to plant cell cultures or microbial production systems, offering candidates to improve the production of natural compounds with unstable supply. Connecting these findings to actual processes requires further validation of enzyme activity, intermediate toxicity, and intercellular transport mechanisms.