Abstract

Knot-free timber production inCunninghamia lanceolatadepends critically on internodal characteristics, yet the mechanisms governing internode elongation remain poorly understood, hindering breeding efforts for longer-internode varieties. In this study, we selected two clones with distinct internodal traits (the C1 clone exhibited a 25.03% longer internodal length than the C11 clone) as materials. Enzyme-linked immunosorbent assay (ELISA) and RNA sequencing were used to investigate dynamics in endogenous hormones and transcriptional regulation in internodal growth. Results showed that the difference in indole-3-acetic acid (IAA) rhythms in apical buds is a key factor of C1’s longer internodal growth; higher levels of IAA and cytokinins in the apical buds of C1 may support sustained internodal growth; upregulated IAA-related genes in upper phloem (PIN1andSAURs), which are involved in polar transport and signal response, indicates a stronger capacity to establish apical dominance. Hormone transport may be regulated by very long-chain fatty acids (VLCFAs). Consistent with reduced brassinosteroid activity, genes involved in VLCFA biosynthesis and transport were generally lower in C1, implying excessive VLCFA accumulation in C11 may be negative to IAA transporting and internode growth. This study offers a preliminary insight into internodal growth mechanisms influenced by hormone biosynthesis and transport inC. lanceolata., providing a basis for genetic improvement, germplasm selection, and exogenous hormone applications in knot-free timber cultivation.