A novel rejuvenation approach to improve rooting capacity and its mechanism in Cunninghamia lanceolata

Chinese fir is the most important evergreen coniferous species for afforestation in subtropical China due to rapid growth and excellent timber quality. Plant cutting propagation plays key role in the vegetative propagation, and is more practical for rejuvenation. This study was focused on understanding the influencing mechanism of adventitious root formation, and we investigated rooting capacity of different scion methods in two different cutting orchards. The results showed that TC (the cuttings from the cutting orchard of "burying trunk with crown") has highest rooting capacity, indicating the cutting orchard has better rejuvenation effect. The ascorbate peroxidase (APX activity), Jasmonic acid (JA) and N-((-)-jasmonoyl)-S-isoleucine [JA-Ile] of cutting phloem were correlated to rooting capacity. The genes involved in the plant hormone signal pathway showed different regulation to rejuvenation, differentially expressed genes (DEGs) in indole-3-acetic acid (IAA) and Brassinosteroid (BR)-related pathway were mostly upregulated, while DEGs in abscisic acid (ABA) and gibberellins (GA)related pathway were mostly downregulated. Phenylpropanoid biosynthesis and terpenoid backbone biosynthesis genes were significantly up-related in roots, the DFR (dihydroflavonol 4-reductase) genes in flavonoid biosynthesis were upregulated in seedlings submitted to treatments with higher degree of rejuvenation with respect to seedlings submitted to lower degree of rejuvenation. Through weighted gene co-expression network analysis (WGCNA) analysis, we identified key genes including SAUR, A-ARR, HDR, HDS and POX. The SEM model indicated different scions directly positively affected rooting, APX activity and HDR gene, and cutting phloem JA negatively affected rooting. These results lay the foundation for further studies on rejuvenation in woody plants, and open new avenues for increasing the efficiency of vegetative propagation of other woody species.