Identification and Characterization of Trihelix Transcription Factors and Expression Changes during Flower Development in Pineapple

Trihelix transcription factors with helix–loop–helix–loop–helix characteristics are essential in plant growth, development, and response to adversity. Several potential functions of Trihelix have been studied in multiple plant species, but little is known about the features and functions of Trihelix genes in pineapple. In this study, 23 Trihelix members were identified and classified into 5 groups and were unevenly distributed in 17 chromosomes of pineapple. The results revealed that six fragment duplication events and one tandem duplication event were found through gene duplication analysis. Moreover, 4, 10, 21, and 23 homologous gene pairs were found between pineapple and Arabidopsis, grape, banana, and rice, respectively. The promoters of Trihelix have many cis-elements, especially in light and hormone response. The expression characteristics of AcTrihelix members showed obvious tissue specificities in different tissues. The expressions of AcTrihelix3, AcTrihelix8, AcTrihelix16, AcTrihelix19, AcTrihelix20, and AcTrihelix23 were maintained at high levels during the late stage of flower bud development. In floral organs, the expression of different members was very different. In conclusion, some AcTrihelix members may play important roles during the floral development of pineapple, and they provide resources for further studies of the function of Trihelix and the molecular mechanism during pineapple flower formation.