GA3 and ABI3 gene expression in coffee seeds during maturation
During maturation in seeds, metabolic processes dependent on gene expression are controlled by hormones, including abscisic acid and gibberellin. These hormones determine dormancy or the capacity for germination in seeds and may have different expression levels in the endosperm and embryo of coffee seeds. We quantified gene expression in the biosynthetic pathway of gibberellin and abscisic acid in different parts of Coffea arabica L. seeds in pre and post physiological maturity, in order to better understand the germination mechanisms of this species. Coffee fruits were harvested at green, yellowish-green, cherry, over-ripe and dry stages. For studies of gene expression, intact seeds were used in addition to endosperm and isolated embryos. The RNA from different tissues was extracted and treated with DNAse to synthesize cDNA. Transition levels of CaGA3 (gibberellin) and CaABI3 (abscisic acid) genes were quantified with qRT-PCR, using specific primers for coffee. Intact seeds at each phenological stage were submitted to germination tests, to evaluate the physiological quality of the seeds. Seed harvested at green and dry stages showed lower physiological quality when compared to the other maturation stages, and germination at the green stage was close to zero. Greatest expression of CaGA3 and CaABI3 occurs in the endosperm of coffee seeds in cherry and over-ripe stages, with better physiological performance. There are differences in CaABI3 and CaGA3 gene expression in embryos and endosperm of the coffee seeds.