Identification and functional verification of PlFT gene associated with flowering in herbaceous peony based on transcriptome analysis

The herbaceous peony (Paeonia lactiflora Pall.) is considered to be a highly valued cut flower plant. It has large flower with rich colors. However, there has been little or no research into the genes related to its flower development. In this study, we used the Illumina HiSeq platform to analyze the RNA-Seq comparative transcriptome of the P. lactiflora 'Dafugui' in three different flowering periods. Nine cDNA libraries were established, from which 92.53 Gb data with 81,788 unigenes were obtained. We screened the genes related to P. lactiflora flowering, isolated and cloned the PlFT gene related to flowering. The total length of the PlFT gene was 592 bp, which had a complete open reading frame of 522 bp and encoded 173 amino acids. The accession number of the PlFT gene is MT249229. To test the role of PlFT, we constructed an expression vector for genetic transformation. Its expression in Arabidposis mutant indicated that PlFT was involved in the flowering of P. lactiflora. This is the first transcriptome analysis of flower development in P. lactiflora. Our results provide some fundamental information for further analyzing the molecular mechanism underlying flower development of P. lactiflora. Citation: Sun J, Chen T, Wu Y, Tao J. 2021. Identification and functional verification of PlFT gene associated with flowering in herbaceous peony based on transcriptome analysis. Ornamental Plant Research 1: 7 https://doi.org/10.48130/OPR-2021-0007 INTRODUCTION The herbaceous peony (Paeonia lactiflora Pall.), a member of the family Paeoniaceae, is a traditional herb flowering plant and has a long history of cultivation in China. It used to grow in the Imperial Palace Garden and is known as the 'PrimeMinister of flowers'[1]. The P. lactiflora flower is elegant and beautiful with a high ornamental value. Its flowers have not only single petal, double petal, golden pistil, crown, and other flower types but also rich colors, such as white, green, pink, and yellow. Regulation of flowering of herbaceous peony can be manipulated in protected cultivation, but the production cost is high. P. lactiflora loses the stems and leaves in autumn but survives in winter as a dormant root mass as the herbaceous peony is deciduous[2]. To break the dormancy of buds in spring, it needs a long time of low temperature during dormancy to meet the winter-cold requirements[3−5]. In addition to the low temperature, application of GA3 can promote flowering[6]. For the early flowering cultivar Dafugui, 4−5 axillary buds on the top of the terminal bud developed into a primordium shape in the overwintering state. 'Dafugui' experiences flower bud differentiation, bract primordium differentiation, petal primordium formation, stamen primordium emergence and development, and pistil primordium formation from early September to April of the following year[7]. Information on flower bud differentiation and flowering regulation of herbaceous peony is helpful to provide the theoretical basis for promoting flowering. Flowering marks the transition from vegetative growth to reproductive growth, and the time of flowering affects a plants commercial value[8]. At the same time, regulation of the flowering period is also essential for plant seed setting. Compared to other species, the molecular mechanism of flowering in Arabidopsis is relatively well understood[9]. In Arabidopsis, there are six response pathways including photoperiod, vernalization, autonomic, temperature, gibberellin, and age pathway, to regulate flowering[10]. Both endogenous and exogenous factors determine the flowering time of plants. Endogenous factors are mainly related to the genes that regulate flowering transformation. For example, FT[11], FLC[12], LFY[13] and SOC1[14] are called flower induction switches. Among them, FT protein is a globular protein with 175 amino acids, both mRNA and FT protein can regulate flowering. FT gene is regarded as a florigen gene[15], which is conservative. It was previously reported that the FT protein could be transported between cells through phloem and transported to the apical meristem, inducing plant flowering[16]. It does not work alone, but interacts with other proteins to regulate flowering. Currently, FT and its homologous genes are found to promote flowering in winter wheat, barley[17], rubber tree[18], rice[19,20], vanda hybrid[21], chrysanthemums[22] and other plants. It is reported that the LFT1 gene of Lilium was most homologous to the AtFT gene and showed peak expression in shoot apices, which promotes flowering in Arabidopsis[23]. The regulation of flowering by FT is also influenced by photoperiod induction and other proteins. Recently, Jing et ARTICLE