GA3 is superior to GA4 in promoting bud endodormancy release in tree peony (Paeonia suffruticosa) and their potential working mechanism

Abstract

Background: Sufficient low temperature accumulation is the key strategy to break bud dormancy and promote subsequent flowering in tree peony anti-season culturing production. Exogenous gibberellins (GAs) could partially replace chilling to accelerate dormancy release, and different kinds of GAs showed inconsistent effects in various plants. To understand the effects of exogenous GA₃ and GA₄ on dormancy release and subsequent growth, the morphological changes were observed after exogenous GAs applications, the differentially expressed genes (DEGs) were identified, and the contents of endogenous phytohormones, starch and sugar were measured, respectively. Results: Morphological observation and photosynthesis measurements indicated that both GA₃ and GA₄ applications accelerated bud dormancy release, but GA₃ feeding induced faster bud burst, higher shoot and more flowers per plant. Full-length transcriptome of dormant bud was used as the reference genome. Totally 124 110 459, 124 015 148 and 126 239 836 reads by illumina transcriptome sequencing were obtained in mock, GA₃ and GA₄ groups, respectively. Compared with the mock, there were 879 DEGs and 2 595 DEGs in GA₃ and GA₄ group, 1 179 DEGs in GA₃ vs GA₄, and 849 DEGs were common in these comparison groups. The significant enrichment KEGG pathways of 849 DEGs highlighted plant hormone signal transduction, starch and sucrose metabolism, cell cycle, DNA replication, etc. Interestingly, the contents of endogenous GA₁, GA₃, GA₄, GA₇ and IAA significantly increased, ABA decreased after GA₃ and GA₄ treatments by LC–MS/MS. Additionally, the soluble glucose, fructose and trehalose increased after exogenous GAs applications. Compared to GA₄ treatment, GA₃ induced higher GA₁, GA₃ and IAA level, more starch degradation to generate more monosaccharide for use, and promoted cell cycle and photosynthesis. Higher expression levels of dormancy-related genes, TFL, FT, EBB1, EBB3 and CYCD, and lower of SVP by GA₃ treatment implied more efficiency of GA₃. Conclusions: Exogenous GA₃ and GA₄ significantly accelerated bud dormancy release and subsequent growth by increasing the contents of endogenous bioactive GAs, IAA, and soluble glucose such as fructose and trehalose, and accelerated cell cycle process, accompanied by decreasing ABA contents. GA₃ was superior to GA₄ in tree peony forcing culture, which might because tree peony was more sensitive to GA₃ than GA₄, and GA₃ had a more effective ability to induce cell division and starch hydrolysis. These results provided the value data for understanding the mechanism of dormancy release in tree peony.