Abstract
To obtain a comprehensive overview of the dynamic transcriptome during male floral bud development in Populus tomentosa, high-throughput RNA-seq was conducted during eight flowering-related stages. Among the 109,212 de novo assembled unigenes, 6,959 were differentially expressed during the eight stages. The overrepresented classed of genes identified by Gene Ontology (GO) enrichment included ‘response to environmental stimuli’ and ‘plant-type spore development’. One-third of the differentially expressed genes were transcription factors (TFs). Several genes and gene families were analyzed in depth, including MADS-box TFs, Squamosa promoter binding protein-like family, receptor-like kinases, FLOWERING LOCUS T/TERMINAL-FLOWER-LIKE 1 family, key genes involved in anther and tapetum development, as well as LEAFY, WUSCHEL and CONSTANS. The results provided new insights into the roles of these and other well known gene families during the annual flowering cycle. To explore the mechanisms regulating poplar flowering, a weighted gene co-expression network was constructed using 98 floral-related genes involved in flower meristem identity and flower development. Many modules of co-expressed genes and hub genes were identified, such as APETALA1 and HUA1. This work provides many new insights on the annual flowering cycle in a perennial plant, and a major new resource for plant biology and biotechnology.
Highlights
Unlike annuals, woody perennials have an extended juvenile phase
In-depth studies of the molecular basis of Populus flower development will contribute to a shortened breeding cycle for helping productivity and an understanding of the complex regulatory mechanisms controlling flowering in poplar
We used paraffin-embedded tissues to examine the morphogenesis of male floral buds in P. tomentosa, and high-throughput sequencing to obtain global gene expression profiles during floral bud development in poplar
Summary
Zhong Chen[1,2], Pian Rao[2], Xiaoyu Yang[2], Xiaoxing Su3, Tianyun Zhao[2], Kai Gao[2], Xiong Yang2 & Xinmin An2,4. To explore the mechanisms regulating poplar flowering, a weighted gene co-expression network was constructed using 98 floral-related genes involved in flower meristem identity and flower development. Flowering is mainly controlled by six different endogenous (autonomous, gibberellin, and age) and environmental (photoperiod, temperature, and vernalization) pathways that together form a complex regulatory network[2] All of these pathways are integrated through the transcriptional regulation of two floral pathway integrators, FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1). Unlike AP1 in Arabidopsis, ectopic expression of LAP1 (a tree ortholog of AP1) fails to induce early flowering in hybrid aspens; LAP1 is instead involved in short-day (SD)-mediated seasonal growth cessation[12]. In-depth studies of the molecular basis of Populus flower development will contribute to a shortened breeding cycle for helping productivity and an understanding of the complex regulatory mechanisms controlling flowering in poplar. The construction of co-expression networks suggested a link between floral genes and the identified hub genes
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