Genes encoding vascular cambium activity of Eucalyptus urophylla × Eucalyptus grandis revealed by transcriptomic analyses

Abstract

Abstract Background: Vascular cambium activities mainly include cambium proliferation and vascular tissue formation through secondary growth, thereby producing new secondary phloem inward and secondary xylem outward and leading to continuous tree thickening and wood for-mation. Therefore, the analysis of the molecular mechanism underlying wood vascular cambium activities can lead to the identification of both key and related genes involved in the for-mation, development, and differentiation of vascular cambium. Results: In the present study, RNA-Seq and Pac-Bio Iso-Seq were used for profiling gene expression changes in Eucalyptus urophylla × E. grandis (E. urograndis) vascular cambium at four different ages. A total of 59,770 non-redundant transcripts and 1892 differentially expressed genes (DEGs) were identified. The expression trends of the DEGs related to cell division and differentiation, cell wall biosynthesis, phytohormone, and transcription factors were analyzed. The DEGs encoding expansin, kinesin, cycline, PAL, GRP9, KNOX, C2C2-dof, REV, etc., were highly expressed in E. urograndis at three years old, leading to positive effects on growth and development. Moreover, some gene family members, such as NAC, MYB, HD-ZIP III, RPK, and RAP, play different regulatory roles in vascular cambium activity because of their sophisticated transcriptional network and function redundantly. Conclusions: These candidate genes are a potential resource to further study vascular cambium activity, espe-cially in fast-growing and adaptable eucalyptus. The results may also serve as a basis for further research to unravel the molecular mechanism underlying wood formation.