Seed coat removal in pear accelerates embryo germination by down-regulating key genes in ABA biosynthesis

Seed coat-induced dormancy protects embryos from environmental conditions, and delays seed germination. In this study, we developed a simple method to accelerate embryo germination. That is, pear seeds were peeled the coats and then put on the humid gauze under 16 h day-light (75 μmol m−2 s−1), the embryo was germinated at 36 h after treatment. This germination results from the reduction of ABA concentration and unrelated to IAA, GA3, and ZR concentrations. Key genes for ABA biosynthesis were isolated and phylogenetically classified for pear. Only PbZEP2, PbZEP3, and PbNECD.C1 were found to be down-regulated in the germinated embryos, while the other genes, such as SDR and AO genes, are not correlated with ABA biosynthesis. Thus, the reduction of ABA concentration in the germinated embryos resulted from the down-regulations of PbZEP2, PbZEP3, and PbNECD.C1 genes. We speculate that the embryo in the pear cultivar Cuiguang is stressed by the seed coat, which leads to an accumulation of ABA in the embryo. We suggest that when abiotic stress of the seed coat is removed, signal transduction of the stresses is terminated and key genes for ABA biosynthesis are down-regulated.

Abbreviations: ABA: Abscisic acid; GA: Gibberellic; ZR: Ribosylzeatin; IAA: auxin; ZEP: Zeaxanthin epoxidase; NCED: 9-cis-epoxycarotenoid dioxygenase; SDR: Short-chain dehydrogenase/reductase; AO: Aldehyde oxidase; MS: Mass spectrometer; ESI: Electrospray ionization; HPLC: High-performance liquid chromatography; qRT-PCR: Quantitative real-time PCR.