To bloom once or more times: the reblooming mechanisms of Iris germanica revealed by transcriptome profiling

Zhuping Fan,Qixiang Zhang,Yike Gao,Rong Liu,Yi Ren,Chunjing Guan

doi:10.1186/s12864-020-06951-x

Abstract

BackgroundThe reblooming bearded iris (Iris germanica) can bloom twice a year, in spring and autumn. The extended ornamental period makes it more popular and brings additional commercial values. However, little is known about the reblooming mechanisms, making the breeding programs time-consuming and labor-wasting. Therefore, a comparative transcriptome profiling was conducted on once-bloomers and rebloomers from the same F1 generation on six development stages, and the candidate genes associated with reblooming were identified.ResultsA total of 100,391 unigenes were generated, the mean length being 785 bp. In the three comparisons (the floral initiation stage of spring flowering in once-bloomers (OB-T1) vs the floral initiation stage of spring flowering in rebloomers (RB-T1); RB-T1 vs the floral initiation stage of autumn flowering in rebloomers (RB-T5); OB-T1 vs RB-T5), a total of 690, 3515 and 2941 differentially expressed genes (DEGs) were annotated against the public databases, respectively. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis focused on the photoperiod response, the temperature insensitivity and the growth speed, to remove the redundant DEGs and figure out the candidate key genes. As a result, the following four genes, PHYTOCHROME A (PHYA), GIGANTEA (GI), SHORT VEGETATIVE PERIOD (SVP) and AUXIN RESPONSE FACTOR (ARF), were considered to be involved in the second floral initiation of the rebloomers.ConclusionThis research provides valuable information for the discovery of the reblooming-related genes. The insights into the molecular mechanisms of reblooming may accelerate the breeding of bearded iris and other perennials.

Highlights

The reblooming bearded iris (Iris germanica) can bloom twice a year, in spring and autumn
Functional annotation of differentially expressed genes (DEGs) Differentially expressed gene (DEG) were filtered from the comparison of three stages, including the floral initiation stage of spring flowering in once-bloomers (OB-The floral initiation stage of spring flowering (T1)), the floral initiation stage of spring flowering (RB-T1) and autumn flowering (RB-The floral initiation stage of autumn flowering (T5)) in rebloomers
In the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, we mainly focused on the “plant hormone signal transduction” under the “environmental information processing” category and the

Summary

Introduction

The reblooming bearded iris (Iris germanica) can bloom twice a year, in spring and autumn. Iris germanica (bearded iris), characterized by the colorful beard on the three falls, is one of the most important perennials in the garden of spring, which can offer a full bloom from April to May [1, 2]. In the long breeding history, some reblooming bearded irises occurred, which could bloom for the second time in autumn of the same. Various studies have revealed the relationship between continuous flowering and the expression of TERMINAL FLOWER1 (TFL1). In Fragaria vesca, a 2-bp deletion in the coding region of the TFL1 homologue introduced a frame shift and reversed the photoperiodic requirement for flowering, generating continuous flowering behavior [11, 12]. The transcription of TFL1 was blocked in continuous flowering roses due to an insertion of retrotransposon, and the absence of the floral repressor TFL1 provoked the continuous blooming [11]

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