Morpho-Histology, Endogenous Hormone Dynamics, and Transcriptome Profiling in Dacrydium Pectinatum during Male Cone Development

Shaojie Huo,Enbo Wang,Xiqiang Song,Zhaoji Li,Yifan Li,Weijuan Zhou,Ying Zhao,Donghua Yang,Mingxun Ren,Jian Wang,Wenju Lu,Haiying Liang

doi:10.3390/f12111598

Abstract

Dacrydium pectinatum de Laubenfels is a perennial gymnosperm species dominant in tropical montane rain forests. Due to severe damages by excessive deforestation, typhoons, and other external forces, the population of the species has been significantly reduced. Furthermore, its natural regeneration is poor. To better understand the male cone development in D. pectinatum, we examined the morphological and anatomical changes, analyzed the endogenous hormone dynamics, and profiled gene expression. The morpho-histological observations suggest that the development of D. pectinatum male cone can be largely divided into four stages: microspore primordium formation (April to May), microspore sac and pollen mother cell formation (July to November), pollen mother cell division (January), and pollen grain formation (February). The levels of gibberellins (GA), auxin (IAA), abscisic Acid (ABA), cytokinin (CTK), and jasmonic acid (JA) fluctuated during the process of male cone development. The first transcriptome database for a Dacrydium species was generated, revealing >70,000 unigene sequences. Differential expression analyses revealed several floral and hormone biosynthesis and signal transduction genes that could be critical for male cone development. Our study provides new insights on the cone development in D. pectinatum and the foundation for male cone induction with hormones and studies of factors contributing to the species’ low rate of seed germination.

Highlights

Dacrydium pectinatum de Laubenfels is a perennial gymnosperm in the family of Podocarpaceae
The initial glimpse into the complexity of the D. pectinatum genome, we found that the GC content of the D. pectinatum transcriptome was 45%, similar to what have been reported in other conifer species, e.g., 47% in Amentotaxus argotaenia [35] and 44.58% in Pinus dabeshanensis [36]
We report that male buds become distinguishable in April in the tropical montane rain forests in China and continue to differentiate and develop until the following March

Summary

Introduction

Dacrydium pectinatum de Laubenfels is a perennial gymnosperm in the family of Podocarpaceae. This evergreen dioecious tree is a dominant species in tropical montane rain forests and native to China (Hainan province), Malaysia (Billiton), Borneo, and Philippines (Luzon and Mindanao) [1]. The wood of D. pectinatum is valuable for constructing buildings and high-grade handcrafting such as ships (http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=210000447, accessed on 1 June 2018). On the coastal plains of Sabah, Sarawak and Kalimantan, 80% of D. pectinatum occupancy area has lost during the massive conversion of lowland forest to oil palm plantations (https://www.iucnredlist.org/, accessed on 5 June 2018). D. pectinatum natural forests have been significantly reduced in China since the 1960s due to severe damages by excessive deforestation, typhoons, and other external forces. According to a report published in 2016 (China Forestry Bureau 2016), only 14,484 hectares are available in China, accounting for 3,473,575 cubic meter of forest volume

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