glyptostroboides due to limited genomic resources. At this time, few studies are available on M. Given the fact that male bud initiation is functionally adapted for successful pollination, exploring the gene expression involved in male reproductive development is important for understanding the molecular regulation of flowering and cone development, and for determining how and why there are few male cones on adult trees. In addition, despite its large numbers and worldwide distribution, most adult trees have low seed viability as a result of inbreeding depression (Li et al., 2005). Few reports have examined male cones (e.g., Jin et al., 2012) because few trees produce them. In the past few decades, there have been studies on morphology and anatomy (Sterling, 1949 Dörken, 2012) however, the majority of these have focused on female cones. It is a monoecious species with male cones and female cones on different twigs of adult trees. Metasequoia glyptostroboides Hu et Cheng, a famous living fossil (also known as the dawn redwood) and the sole extant species of Metasequoia, which has been merged with Cupressaceae as the subfamily Sequoia (Brunsfeld et al., 1994), is found in the Hubei and Hunan provinces in south-central China, and has been widely distributed in the Northern Hemisphere (Nelson, 1998 Kunzmann and Mai, 2011).Īlthough of great ecologic and economic importance, like most gymnosperm trees, Metasequoia has a long juvenile phase (20–30 years) before female bud appearance, making their seeds scarce. In addition, these studies on hormone-mediated sugar pathways increase our understanding of the relationship between sugar and hormone signaling during female and male bud initiation in Metasequoia. Our results increase our understanding of the reproductive bud transition in gymnosperms. Key enzymes were identified in these pathways, including alcohol dehydrogenase ( NAD) and glutathione dehydrogenase for the glycolysis/gluconeogenesis pathway, and glucanphosphorylase for sucrose and starch metabolism pathways. Among the significantly changed pathways, sugar pathways were mediated by hormone signals during the vegetative-to-reproductive phase transition, including glycolysis/gluconeogenesis and sucrose and starch metabolism pathways. These differentially expressed transcripts were associated with 243 KEGG pathways. Next, 32 differentially and specifically expressed transcripts were determined using quantitative real-time polymerase chain reaction, including the upregulation of MADS-box transcription factors involved in male bud transition and flowering time control proteins involved in female bud transition. Samples from hormone-treated cone reproductive shoots and naturally occurring non-cone setting shoots were analyzed using 24 digital gene expression (DGE) tag profiles using Illumina, generating a total of 69,520 putative transcripts. In the current study, hormone-treated shoots found in female and male buds were used to identify candidate genes involved in reproductive bud transition in Metasequoia. Previously, we induced reproductive buds using a hormone solution in juvenile Metasequoia trees as young as 5-to-7 years old. Metasequoia glyptostroboides is a famous redwood tree of ecological and economic importance, and requires more than 20 years of juvenile-to-adult transition before producing female and male cones.
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