Unravelling molecular mechanisms underlying growth-promoting effects of gibberellic acid (GA3) on 'Da Hong Tian' cultivar of pomegranate (Punica granatum L.)

• GA 3 is predominant bioactive GA compound in 'Da Hong Tian' cultivar of pomegranate. • Foliar GA 3 treatments increase vegetative growth of 'Da Hong Tian' plantlets. • Gene expression of cell division and phytohormone crosstalk are altered by GA 3 spray. • GA 3 -induced growth and gene expression changes are in a dose-dependent manner. Gibberellins (GAs) are one kind of typical endogenous plant growth regulators, and have been widely used for improving the growth and development of hardwood cuttings of pomegranate. However, our knowledge on the mechanisms behind GA-induced growth promotion in pomegranate is largely unknown. In the current study, we administered foliar spray of gibberellic acid (GA 3 ) on 'Da Hong Tian' cultivar of pomegranate, and the GA 3 -treated plantlets displayed higher plant height, longer internode length, more new leaves and increased soluble sugar and chlorophyll contents, demonstrating the promoting effects of exogenous GA 3 application on the vegetative growth of 'Da Hong Tian' pomegranate. Genes associated with cell division and growth, plant organ morphogenesis and development, cell wall biogenesis and modification and endogenous phytohormone-mediated signaling transduction were significantly differentially expressed upon GA 3 treatments, which facilitated new leaf growth and internode elongation. More importantly, GA 3 -induced expression alterations of the genes pertaining to cell proliferation and growth, and endogenous phytohormone biosynthesis and crosstalk displayed a dose-dependent manner, which could be responsible for the growth and development advantages of the plantlets supplied with a higher concentration (80 mg/L) of GA 3 . These findings unravel the molecular mechanisms that regulate the promoting effects of GA 3 on the vegetative growth of 'Da Hong Tian' pomegranate and provide a theoretical guidance to the external GA application for improving orchard cultivation of pomegranate.