Transcriptome and physiological analyses provide insights into the leaf epicuticular wax accumulation mechanism in yellowhorn

Yang Zhao,Mengke Wang,Quanxin Bi,Yifan Cui,Xiaojuan Liu,Libing Wang

doi:10.1038/s41438-021-00564-5

Abstract

Plantations and production of yellowhorn, one of the most important woody oil and urban greening trees widely cultivated in northern China, have gradually become limited by drought stress. The epicuticular wax layer plays a key role in the protection of yellowhorn trees from drought and other stresses. However, there is no research on the mechanism of wax loading in yellowhorn trees. In this study, we investigated the anatomical and physiological characteristics of leaves from different germplasm resources and different parts of the same tree and compared their cuticle properties. In addition, the different expression patterns of genes involved in wax accumulation were analyzed, and a coexpression network was built based on transcriptome sequencing data. Morphological and physiological comparisons found that the sun leaves from the outer part of the crown had thicker epicuticular wax, which altered the permeability and improved the drought resistance of leaves, than did shade leaves. Based on transcriptome data, a total of 3008 and 1324 differentially expressed genes (DEGs) were identified between the sun leaves and shade leaves in glossy- and non-glossy-type germplasm resources, respectively. We identified 138 DEGs involved in wax biosynthesis and transport, including structural genes (such as LACS8, ECH1, and ns-LTP) and transcription factors (such as MYB, WRKY, and bHLH transcription factor family proteins). The coexpression network showed a strong correlation between these DEGs. The differences in gene expression patterns between G- and NG-type germplasm resources under different light conditions were very clear. These results not only provide a theoretical basis for screening and developing drought-resistant yellowhorn germplasm resources but also provide a data platform to reveal the wax accumulation process of yellowhorn leaves.

Highlights

Yellowhorn (Xanthoceras sorbifolium Bunge) is one of the most important species of woody oil and greening trees and has been widely cultivated in northern China in recent years
The chlorophyll leaching assays revealed a major difference in the cuticle permeability of sun leaves and shade leaves from G- and NG-type germplasm resources due to their different levels of wax accumulation (Fig. 2a)
Simple linear correlation analysis indicates that the water loss speed is related to the wax thickness (R2 = 0.92) and wax content (R2 = 0.96) (Supplementary Fig. S3). These results suggest that cuticular wax has an important role in protecting leaves from water loss; drought resistance and cuticular permeability of leaves could be altered with an increase in wax accumulation due to the variation in light conditions

Summary

Introduction

Yellowhorn (Xanthoceras sorbifolium Bunge) is one of the most important species of woody oil and greening trees and has been widely cultivated in northern China in recent years. As an endemic species to China, yellowhorn has high medicinal and ornamental value and important socioeconomic value due to its high fatty acid content[1]. Plants, including yellowhorn, have evolved various strategies to respond and adapt to drought stress through their long evolutionary history. Among these strategies, cuticles form the primary essential barrier for decreasing nonstomatal water loss under drought stress[3]. The cuticle is a unique structure developed by land plants.

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