Abstract
Gibberellins (GAs) are an important group of phytohormones associated with diverse growth and developmental processes, including cell elongation, seed germination, and secondary growth. Recent genomic and genetic analyses have advanced our knowledge of GA signaling pathways and related genes in model plant species. However, functional genomics analyses of GA signaling pathways in Panax ginseng, a perennial herb, have rarely been carried out, despite its well-known economical and medicinal importance. Here, we conducted functional characterization of GA receptors and investigated their physiological roles in the secondary growth of P. ginseng storage roots. We found that the physiological and genetic functions of P. ginseng gibberellin-insensitive dwarf1s (PgGID1s) have been evolutionarily conserved. Additionally, the essential domains and residues in the primary protein structure for interaction with active GAs and DELLA proteins are well-conserved. Overexpression of PgGID1s in Arabidopsis completely restored the GA deficient phenotype of the Arabidopsis gid1a gid1c (atgid1a/c) double mutant. Exogenous GA treatment greatly enhanced the secondary growth of tap roots; however, paclobutrazol (PCZ), a GA biosynthetic inhibitor, reduced root growth in P. ginseng. Transcriptome profiling of P. ginseng roots revealed that GA-induced root secondary growth is closely associated with cell wall biogenesis, the cell cycle, the jasmonic acid (JA) response, and nitrate assimilation, suggesting that a transcriptional network regulate root secondary growth in P. ginseng. These results provide novel insights into the mechanism controlling secondary root growth in P. ginseng.
Highlights
These results indicate that GA facilitates root secondary growth in P. ginseng by promoting storage parenchyma cell development
All complementation lines expressing P. ginseng gibberellin-insensitive dwarf1s (PgGID1s) showed a wildtype shoot phenotype (Figure 3A) and partially enhanced silique length compared with Atgid1a/c plants (Figure 3B). These results indicate that PgGID1s can replace the function of AtGID1s during plant growth and development
We successfully identified GA receptor-encoding genes expressed by P. ginseng based on whole-genome sequence and transcriptomic data and characterized their physiological responses during root secondary growth
Summary
Recent studies have shown that there are complicated internal and external signaling interactions of GAs and various hormone pathways, including auxin, abscisic acid (ABA), jasmonic acid (JA), ethylene, and cytokinin. These interactions are highly relevant to plant growth, development, and stress tolerance [12,13,14]. In the presence of GA, DELLA is recognized by the SCFSLY1/GID2 ubiquitin E3 ligase complex for subsequent 26S proteasome-meditated degradation [21,23,24] This canonical GA signaling pathway is responsible for various physiological responses during plant growth and development
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