Transcriptome profiling of Indole-3-Butyric Acid-Induced Adventitious Root Formation in softwood Cuttings of walnut

Inducing adventitious root (AR) formation in mature walnut species ( L.) is challenging. However, the AR formation of mature trees can be improved by rejuvenation. In rejuvenated cuttings, exogenous indole-3-butyric acid (IBA) is essential for AR formation, and the underlying mechanism is still not well understood. Therefore, we utilized transcriptome sequencing to investigate the mechanism of IBA-induced AR formation. Our results revealed that, in comparison to the control group, IBA treatment (9 mM) significantly increased the endogenous indole-3-acetic acid (IAA) content, leading to an enhanced rooting rate. We performed RNA sequencing to identify differentially expressed genes (DEGs) between the IBA-treated and control (CK) groups at 1, 2, 3, and 5 days after cutting (DAC). The results showed that, compared to the control cuttings, there were 1 539, 889, 785, and 984 up-regulated genes and 2 791, 2 936, 3 017, and 1 752 down-regulated genes, at 1, 2, 3, and 5 DAC, respectively. Analysis of RNA-seq data revealed that (/) and (), associated with IBA transport, were down-regulated in the rejuvenation cuttings. In contrast, () and (), associated with auxin efflux, were up-regulated. We identified 49 ()-encoding genes, including , , , , , , , , and , which were up-regulated at 1–5 DAC in the rejuvenated cuttings. This study highlights that the overexpression of in poplar significantly enhance AR growth, as evidenced by increased root length, surface area, volume, and quantity. Moreover, the co-expression network analysis involving and in walnut cuttings elucidates complex genetic interactions, underscoring their pivotal role in the formation of AR. Our data supported the following molecular mechanism of IBA-induced adventitious root formation. Firstly, IBA is converted to free IAA in peroxisomes. Then, the highly concentrated IAA in the procambium and parenchyma cells induces