A team of researchers led by Bert De Rybel (VIB-UGent Center for Plant Systems Biology) discovers that a single transcriptional complex, called TMO5/LHW, coordinates vascular development in the plant root meristem by controlling cytokinin levels in space and time. Based on these insights, targeted modulation of specific tissue types in plant roots could lead to more efficient water usage and promote drought resistance.
Patterning of the different tissues and organs is extremely important during plant growth. The vasculature for example is arranged in a bilateral symmetry and consists of multiple cell types each with a specific function during plant development. The central xylem axis transports absorbed water and minerals upwards whereas the flanking phloem poles contribute to water storage and supply of leaf-produced sugars to the roots. Because of its complex composition, the vasculature serves as an excellent model system to study patterning. Correct tissue patterning largely depends on controlled cell division. One of the major regulators of cell division is the phytohormone cytokinin. It however remained unclear how appropriate cytokinin levels are maintained in each of the different cell types in the context of growing tissue.
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Earlier research indicates that the transcription factor complex formed by TARGET OF MONOPTEROS 5 and LONESOME HIGHWAY (TMO5/LHW) plays an important role in controlling vascular growth and patterning.
Picture showing a plant root meristem with distinct hormonal responses in different cell types. The colors depict the nuclei of the root meristem cells.
“In this study, we uncovered that TMO5/LHW triggers local cytokinin biosynthesis in xylem cells through the activation of two cooperating enzymes,” says BaoJun Yang. Together with the lab of Yvan Saeys (VIB-UGent Center for Inflammation Research), transcriptomic changes after increasing cytokinin concentrations were profiled at the single-cell level. The data revealed enhanced expression of CYTOKININ OXIDASE 3 in the vascular tissue adjacent to the xylem, leading to subsequent cytokinin degradation. “Altogether we found that one transcription factor complex regulates vascular tissue development by controlling cytokinin levels in space and time via sequential induction and repression modules.”
Modulating phytohormone levels in space and time for better water management
Understanding how hormone levels are controlled is of great importance to fully grasp the complex function of these molecules in the context of a multi-cellular structure undergoing growth. This is particularly important with plants that continue to grow throughout their lifetime. Once we understand these processes in sufficient detail, we can start to control cell division rate. Although this could lead to faster-growing plants, modulation of specific tissue types holds the greatest promise. “Once we understand how plants control cell divisions in a spatiotemporal manner, we can try to specifically trigger growth in one tissue type,” says Bert De Rybel. “Increasing water storage capacity would help plants to overcome extended periods of drought.”
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