Gibberellin Signaling Is Required for Far-Red Light-Induced Shoot Elongation in Pinus tabuliformis Seedlings

Gibberellin (GA) is known to play an important role in low red/far-red (R:FR) light ratio-mediated hypocotyl and petiole elongation in Arabidopsis (Arabidopsis thaliana). However, the regulatory relationship between low R:FR and GAs remains unclear, especially in gymnosperms. To increase our understanding of the molecular basis of low R:FR-mediated shoot elongation in pines and to determine whether there is an association between low R:FR and GAs action, we explored the morphological and transcriptomic changes triggered by low R:FR, GAs, and paclobutrazol (PAC), a GAs biosynthesis inhibitor, in Pinus tabuliformis seedlings. Transcriptome profiles revealed that low R:FR conditions and GAs have a common set of transcriptional targets in P. tabuliformis. We provide evidence that the effect of low R:FR on shoot elongation in P. tabuliformis is at least partially modulated by GAs accumulation, which can be largely attenuated by PAC. GAs are also involved in the cross talk between different phytohormones in the low R:FR response. A GA biosynthesis gene, encoding entkaurenoic acid oxidase (KAO), was strongly stimulated by low R:FR without being affected by GAs feedback regulation or the photoperiod. We show that GA signaling is required for low R:FR-induced shoot elongation in P. tabuliformis seedlings, and that there are different regulatory targets for low R:FR-mediated GA biosynthesis between conifers and angiosperms.