Researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences, together with their collaborators, have created the first single-nucleus transcriptomic landscape of the caper spurge (Euphorbia lathyris), a latex-producing Euphorbia species with bioenergy potential. This high-resolution genetic map has uncovered the molecular mechanisms that restrict the plant's natural rubber production.

Published in Industrial CropsandProducts, the study resolves a long-standing question. Despite possessing a well-developed laticifer system rich in triterpenoids, Euphorbia lathyris has an extremely low capacity to synthesize natural rubber. The study identifies a specific genetic shortfall and a key regulatory switch that together explain this low-yield, low-molecular-weight rubber system.

Using single-nucleus RNA sequencing (snRNA-seq), the researchers mapped the differentiation trajectory of laticifers in young and mature leaves. While these cells actively produce triterpenoids via the mevalonate (MVA) pathway, the machinery for rubber production is notably underpowered.

Through comparative analysis, the researchers revealed the genetic basis for this low yield. The Euphorbia lathyris genome possesses a streamlined repertoire of rubber biosynthesis genes. Crucially, it entirely lacks Hevea-like rubber elongation factors (REFs), which are essential for producing high-molecular-weight rubber. Furthermore, the few rubber-related genes present, such as ElCPT1, are expressed at much lower levels than the triterpenoid synthesis genes in the same laticifers.

The researchers also identified a laticifer-specific transcription factor named COGWHEEL1 (ElCOG1). Functional validation demonstrated that ElCOG1 binds to the promoters of both the rubber synthase gene ElCPT1 and the triterpene synthase gene ElBUT1, thereby actively suppressing their activity.

"This single transcription factor acts as a shared negative control point on both the rubber-elongation and triterpenoid branches of metabolism. This suggests that in caper spurge, the plant actively holds back rubber production rather than simply lacking the ability to produce it," said SUN Guiling of XTBG.

The study not only clarifies the metabolic specialization mechanisms of Euphorbia lathyris laticifers but also provides a methodological framework for deciphering regulatory programs in the secretory cells of other latex-producing plants.