Triacylglycerol biosynthesis in shaded seeds of tung tree (Vernicia fordii) is regulated in part by Homeodomain Leucine Zipper 21

Authors: ZHANG, LINGLING - Wuhan Botanical Garden; LI, WENGYING - Central South University Of Forestry And Technology; FENG, TAO - Hubei University; WU, PAN - Hubei University; Shockey, Jay; CHEN, LIANG - Wuhan Botanical Garden; ZHANG, LIN - Central South University Of Forestry And Technology; LU, SHIYOU - Hubei University

Submitted to: The Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2021
Publication Date: 10/28/2021
Citation: Zhang, L., Wu, P., Li, W., Feng, T., Shockey, J., Chen, L., Zhang, L., Lu, S. 2021. Triacylglycerol biosynthesis in shaded seeds of tung tree (Vernicia fordii) is regulated in part by Homeodomain Leucine Zipper 21. The Plant Journal. 15540. 108(6):1735-1753. https://doi.org/10.1111/tpj.
DOI: https://doi.org/10.1111/tpj.15540

Interpretive Summary: Light is a central signal to all aspects of plant growth and development. As a driver of photosynthesis in green plants, light is the fuel for all life on earth. The details of how light signals are sensed and turned into genetic action inside plant cells has been studied for decades. The role of light in the growth and timing of changes in roots, leaves, flowers, and many other plant organs and tissues is still under investigation in laboratories around the world, but one aspect of plant metabolism has been particularly mysterious in regards to its connection to light: seed oil biosynthesis. In this study, a clear and direct connection is established between proteins that convey the quantity and quality of light shining on tung tree fruits, and the targets of these proteins, which in this case is at least two tung genes that control the quality and quantity of seed oil. This study will provide a template to further expand studies of the links between light and oil production in seeds, and may help to guide agronomic practices, such as tree planting density, that could improve nut and oil value by tree nut growers and producers.

Technical Abstract: Light quantity and quality affects many aspects of plant growth and development. However, few reports have addressed the response of seed oil accumulation to changes in light conditions, especially dense shade. Shade-avoiding plants can redirect plant resources into extension growth at the expense of leaf and root expansion in an attempt to overgrow its neighbors and reach areas containing richer light. In this study, we report that tung oil accumulation is suppressed by dense shade during the rapid oil accumulation phase of seed development. Transcriptome analysis confirmed that dense shade suppression of oil accumulation was attributed to reduced expression of fatty acid and TAG biosynthesis related genes. Through weighted gene co-expression network analysis (WGCNA), we identified 32 core transcription factors (TF) that were specifically up-regulated in densely shaded seeds during the rapid oil accumulation period. Among these, VfHB21, a class I homeodomain leucine zipper (HD-ZIP I) transcription factor, was shown to suppress expression of VfFAD2 and VfFADX, two key genes related to a-eleostearic acid and total seed oil production, by directly binding to their respective promoter regions. This study reveals some of the regulatory mechanisms that control tung tree seed oil biosynthesis specifically, and more broadly, plant storage carbon partitioning in response to dense shade conditions.