Abstract
Cyclanilide (CYC), a plant growth regulator, is a potent shoot branching agent in apple. However, its mechanism remains unclear. The current study revealed that CYC treatment resulted in massive reprogramming of the axillary bud transcriptome, implicating several hormones in the response. We observed a marked increase (approximately 2-fold) in the level of zeatin riboside and a significant decrease (approximately 2-fold) in the level of abscisic acid (ABA). Zeatin metabolism gene cytokinin (CTK) oxidase 1 (CKX 1) was down-regulated at 168 h after CYC treatment compared with the control. Weighted gene co-expression network analysis of differentially expressed genes demonstrated the turquoise module clusters exhibited the highest positive correlation with zeatin riboside (r = 0.92) and the highest negative correlation with ABA (r = −0.8). A total of 37 genes were significantly enriched in the plant hormone signal transduction pathway in the turquoise module. Among them, the expressions of CTK receptor genes WOODEN LEG and the CTK type-A response regulators genes ARR3 and ARR9 were up-regulated. ABA signal response genes protein phosphatase 2C genes ABI2 and ABI5 were down-regulated in lateral buds after CYC treatment at 168 h. In addition, exogenous application of 6-benzylaminopurine (6-BA, a synthetic type of CTK) and CYC enhanced the inducing effect of CYC, whereas exogenous application of lovastatin (a synthetic type of inhibitor of CTK biosynthesis) or ABA and CYC weakened the promoting effect of CYC. These results collectively revealed that the stimulation of bud growth by CYC might involve CTK biosynthesis and signalling, including genes CKX1 and ARR3/9, which provided a direction for further study of the branching promoting mechanism of CYC.
Highlights
Cyclanilide (CYC) is a plant growth regulator which is registered for use in cotton growth control at different development stages, but only in combination with other plant growth regulators, such as ethephon for defoliation [1]
At A-1, the bud length was significantly different from the control on the 8th day, and the branching phenotype with a shoot length of about 14 mm was visible on the 16th day after CYC treatment
At A-3, the bud length was significantly different between CYC treatment and control on the 16th day, no sign of bud outgrowth was observed with a bud length of less than 7 mm (Figure 1b)
Summary
Cyclanilide (CYC) is a plant growth regulator which is registered for use in cotton growth control at different development stages, but only in combination with other plant growth regulators, such as ethephon for defoliation [1]. One is referred to as the “second messenger” model, where auxin in the main stem regulates the synthesis of cytokinins (CTKs) and strigolactones (SLs) that move up into the buds and control their activity. CTKs act as bud outgrowth inducers that antagonise auxin on branching [10,11]. SLs act as bud outgrowth repressors and enhance the inhibitory effect of auxin on branching [12]. Sucrose is an early regulator of the key hormonal mechanisms controlling rose bud outgrowth [18] and sugar prevents auxin, and strigolactone pathways to promote bud outgrowth [19]. BRC1 expression is related to bud inhibition in several species, and its transcript level can be up-regulated by SLs and down-regulated by CTKs [21]. The molecular mechanism of axillary bud growth regulation by CYC is still unclear in apple. The result provided a direction for further study of the branching promoting mechanism of CYC
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
