Unveiling the GA4-Ferulic Acid Regulatory Axis: Redox-Mediated Suberization Governs Adventitious Rooting Recalcitrance in Pinus massoniana

TL;DR

The study identifies a new regulatory pathway involving GA4 and ferulic acid that affects root development in Pinus massoniana, offering a solution to improve rooting success in conifers.

Contribution

The discovery of the GA4-ferulic acid regulatory axis and its role in controlling suberization and root development in conifers is novel.

Findings

PBZ treatment significantly improved rooting success and reduced rooting time in Pinus massoniana.

GA4 accumulation triggered suberization via ferulic acid-mediated redox imbalance, impairing root development.

The combination of PBZ and FA synergistically enhanced rooting success and field survival in conifers.

Abstract

Pinus massoniana, a critically important afforestation species in subtropical China, shows severe adventitious rooting recalcitrance linked to endogenous gibberellin (GA) dysregulation. Our study reveals a GA4-mediated regulatory network that coordinates hormonal crosstalk, redox homeostasis, and cell wall remodeling. Treatment with the GA biosynthesis inhibitor paclobutrazol (PBZ, 100 mg·L−1) shortened rooting time by 32.5% and increased rooting success by 79.5%. We found that PBZ redirected GA flux by upregulating GA3-oxidase (GA3OX), leading to GA4 accumulation. However, elevated GA4 levels impaired root development by triggering suberization through ferulic acid (FA)-mediated redox imbalance. Application of GA4 (100 mg·L−1) reduced caffeoyl alcohol content by 54.4% but increased FA and caffeic acid levels 2.4–3.9-fold, shifting lignin precursors toward suberin biosynthesis. FA modulated H2O2 flux in a dose-dependent manner: 200 mg·L−1 optimized redox homeostasis (93.7% lower H2O2 influx), whereas 1000 mg·L−1 suppressed mitosis. The combination of PBZ (100 mg·L−1) and FA (200 mg·L−1) synergistically enhanced rooting success by 34.4% and achieved 95.8% field survival after two years (vs. 68.5% in controls), challenging the traditional view that lignification alone limits rooting in woody plants. This work provides the first evidence that the GA4-FA axis controls adventitious root formation in conifers via a Reactive oxygen species (ROS)-dependent switch between suberin and lignin metabolism, offering new strategies to overcome rooting barriers. The PBZ + FA protocol enables scalable clonal propagation of recalcitrant conifers, with potential applications in molecular breeding and forest restoration.

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