Digital gene expression analysis of male and female bud transition in Metasequoia reveals high activity of MADS-box transcription factors and hormone-mediated sugar pathways.

Ying Zhao,Congpeng Wang,Haiying Liang,Lan Li,Xiao Han,Xinli Xia,Sha Tang,Weilun Yin

doi:10.3389/fpls.2015.00467

Ying Zhao, Congpeng Wang + Show 6 more

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https://doi.org/10.3389/fpls.2015.00467

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Abstract

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. Previously, we induced reproductive buds using a hormone solution in juvenile Metasequoia trees as young as 5-to-7 years old. 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. 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. 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. These differentially expressed transcripts were associated with 243 KEGG 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. 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. Our results increase our understanding of the reproductive bud transition in gymnosperms. 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.

Highlights

Metasequoia glyptostroboides Hu et Cheng, a famous living fossil 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). 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
We found a decrease in the transcript isotig33092 putatively encoding Agamous-like MADS-box protein (AGL21) in CK4 when compared to CK2
To expand our understanding of the gene expression network involved in the transition from vegetative to reproductive phases in Metasequoia, tag sequencing was used as a tool to mine genes (Marioni et al, 2008), because it performs better in gene discovery and has a higher dynamic range (Robinson et al, 2010)

Summary

Introduction

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 It is a monoecious species with male cones and female cones on different twigs of adult trees. 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. At this time, few studies are available on M. glyptostroboides due to limited genomic resources. Metasequoia behind lagged behind other gymnosperm species such as Norway spruce, White spruce, and loblolly pine in genomic resources (Birol et al, 2013; Nystedt et al, 2013; Neale et al, 2014; Zimin et al, 2014)

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