Expression Patterns and Regulation of Non-Coding RNAs during Synthesis of Cellulose in Eucalyptus grandis Hill

Abstract

Cellulose, an essential structural component in the plant cell wall and a renewable biomass resource, plays a significant role in nature. Eucalyptus’s excellent timber tree species (including Eucalyptus grandis Hill) provide many raw materials for the paper and wood industries. The synthesis of cellulose is a very complex process involving multiple genes and regulated by various biological networks. However, research on regulating associated genes and non-coding RNAs during cellulose synthesis in E. grandis remains lacking. In this study, the wood anatomical characteristics and chemical indexes of E. grandis were analyzed by taking three different parts (diameter at breast height (DBH), middle and upper part of the trunk) from the main stem of E. grandis as raw materials. The role of non-coding RNAs (Long non-coding RNA, lncRNA; Micro RNA, miRNA; Circle RNA, circRNA) on regulating candidate genes was presented, and the network map of ceRNA (Competing endogenous RNA) regulation during wood cellulose biosynthesis of E. grandis was constructed. The transcriptome sequencing of nine samples obtained from the trunk of the immature xylem in E. grandis at DBH, middle and upper parts had a 95.81 G clean reading, 57,480 transcripts, 7365 lncRNAs, and 5180 circRNAs. Each sample had 172–306 known miRNAs and 1644–3508 new miRNAs. A total of 190 DE-lncRNAs (Differentially expressed long non-coding RNAs), 174 DE-miRNAs (Differentially expressed micro RNAs), and 270 DE-circRNAs (Differentially expressed circle RNAs) were obtained by comparing transcript expression levels. Four lncRNAs and nine miRNAs were screened out, and the ceRNA regulatory network was constructed. LncRNA1 and lncRNA4 regulated the genes responsible for cellulose synthesis in E. grandis, which were overexpressed in 84K (Populus Alba × Populus glandulosa) poplar. The cellulose and lignin content in lncRNA4-oe were significantly higher than wild type 84K poplar and lncRNA1-oe. The average plant height, middle and basal part of the stem diameter in lncRNA4-oe were significantly higher than the wild type. However, there was no significant difference between the growth of lncRNA1-oe and the wild type. Further studies are warranted to explore the molecular regulatory mechanism of cellulose biosynthesis in Eucalyptus species.