Abstract
Sterile and fertile flowers are an important evolutionary developmental (evo-devo) phenotype in angiosperm flowers, playing important roles in pollinator attraction and sexual reproductive success. However, the gene regulatory mechanisms underlying fertile and sterile flower differentiation and development remain largely unknown. Viburnum macrocephalum f. keteleeri, which possesses fertile and sterile flowers in a single inflorescence, is a useful candidate species for investigating the regulatory networks in differentiation and development. We developed a de novo-assembled flower reference transcriptome. Using RNA sequencing (RNA-seq), we compared the expression patterns of fertile and sterile flowers isolated from the same inflorescence over its rapid developmental stages. The flower reference transcriptome consisted of 105,683 non-redundant transcripts, of which 5,675 transcripts showed significant differential expression between fertile and sterile flowers. Combined with morphological and cytological changes between fertile and sterile flowers, we identified expression changes of many genes potentially involved in reproductive processes, phytohormone signaling, and cell proliferation and expansion using RNA-seq and qRT-PCR. In particular, many transcription factors (TFs), including MADS-box family members and ABCDE-class genes, were identified, and expression changes in TFs involved in multiple functions were analyzed and highlighted to determine their roles in regulating fertile and sterile flower differentiation and development. Our large-scale transcriptional analysis of fertile and sterile flowers revealed the dynamics of transcriptional networks and potentially key components in regulating differentiation and development of fertile and sterile flowers in Viburnum macrocephalum f. keteleeri. Our data provide a useful resource for Viburnum transcriptional research and offer insights into gene regulation of differentiation of diverse evo-devo processes in flowers.
Highlights
Flower development is attracting great attention as a fascinating topic for studying plant development and evolution
We further found that the levels of the LAT52, SF3, and callose synthase 5 (CALS5) remained low in S1 and S2 and increased significantly from S2 to S3 in fertile flowers, whereas ABORTED MICROSPORES (AMS) showed highest expression in S1 and was almost undetectable in S2 and S3, indicating that LAT52, SF3, and CALS5 are involved in maintaining pollen and tapetum development, and AMS made a greater contribution to regulating early tapetum development of fertile flowers than of sterile flowers
Because the fertile flowers of V. macrocephalum f. keteleeri possess normal pistils and stamens, vs. the sterile flowers with abnormal reproductive components, we considered that some differentially expressed genes (DEGs) between fertile and sterile flowers would be associated with reproductive processes and/or plant fertility
Summary
Flower development is attracting great attention as a fascinating topic for studying plant development and evolution. Many sterile flowers are far larger and more conspicuous than fertile flowers within the same inflorescence (Nielsen et al, 2002; Donoghue et al, 2003; Jin et al, 2010) Such sterile flowers exist in many genera, including Viburnum (Adoxaceae) and Hydrangea (Hydrangeaceae), and in the Asteraceae family, and are considered to be an evolutionary consequence of longterm ecological selection by pollinator attraction, which plays an important role in enhancing reproductive success (Donoghue et al, 2003; Jin et al, 2010). The developmental regulation of sterile flowers, which makes them conspicuously different from fertile flowers in appearance and structure, remains unclear
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