Abstract
BackgroundFraxinus hupehensis is an endangered tree species that is endemic to in China; the species has very high commercial value because of its intricate shape and potential to improve and protect the environment. Its seeds show very low germination rates in natural conditions. Preliminary experiments indicated that gibberellin (GA3) effectively stimulated the seed germination of F. hupehensis. However, little is known about the physiological and molecular mechanisms underlying the effect of GA3 on F. hupehensis seed germination.ResultsWe compared dormant seeds (CK group) and germinated seeds after treatment with water (W group) and GA3 (G group) in terms of seed vigor and several other physiological indicators related to germination, hormone content, and transcriptomics. Results showed that GA3 treatment increases seed vigor, energy requirements, and trans-Zetain (ZT) and GA3 contents but decreases sugar and abscisic acid (ABA) contents. A total of 116,932 unigenes were obtained from F. hupehensis transcriptome. RNA-seq analysis identified 31,856, 33,188 and 2056 differentially expressed genes (DEGs) between the W and CK groups, the G and CK groups, and the G and W groups, respectively. Up-regulation of eight selected DEGs of the glycolytic pathway accelerated the oxidative decomposition of sugar to release energy for germination. Up-regulated genes involved in ZT (two genes) and GA3 (one gene) biosynthesis, ABA degradation pathway (one gene), and ABA signal transduction (two genes) may contribute to seed germination. Two down-regulated genes associated with GA3 signal transduction were also observed in the G group. GA3-regulated genes may alter hormone levels to facilitate germination. Candidate transcription factors played important roles in GA3-promoted F. hupehensis seed germination, and Quantitative Real-time PCR (qRT-PCR) analysis verified the expression patterns of these genes.ConclusionExogenous GA3 increased the germination rate, vigor, and water absorption rate of F. hupehensis seeds. Our results provide novel insights into the transcriptional regulation mechanism of effect of exogenous GA3 on F. hupehensis seed germination. The transcriptome data generated in this study may be used for further molecular research on this unique species.
Highlights
Fraxinus hupehensis is an endangered tree species that is endemic to in China; the species has very high commercial value because of its intricate shape and potential to improve and protect the environment
Eleven differentially expressed genes (DEGs) (PGM, three glucose-6-phosphate isomerase (GPI), PFK, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), two Phosphoglycerate kinase (PGK), phosphoglycerate mutase (PGAM), ENO, and pyruvate kinase (PK)) involved in the glycolytic pathway were identified from the RNA-seq data, which implied that exogenous GA3 up-regulated these key genes to convert a-D-glucose-1P into pyruvate, which is the final product of the glycolytic pathway and is used for the metabolic conversion of intermediates in other substances (Fig. 9)
Transcriptomics approaches were used to study the effects of GA3 on F. hupehensis seed germination
Summary
Fraxinus hupehensis is an endangered tree species that is endemic to in China; the species has very high commercial value because of its intricate shape and potential to improve and protect the environment. Preliminary experiments indicated that gibberellin (GA3) effectively stimulated the seed germination of F. hupehensis. Little is known about the physiological and molecular mechanisms underlying the effect of GA3 on F. hupehensis seed germination. Fraxinus hupehensis Chu, Shang et Su. is a woody plant of the Oleaceae family that is officially listed as a national rare and endangered tree species in China [1,2,3]. The species has high commercial value due to its slow growth, interlaced roots, intricate tree shape, and easy to shape. F. hupehensis seeds take more than 1 year of dormancy to germinate [9]. Its resources should be protected, and its reproductive and growth cycles should be accelerated through artificial technologies
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