Transcriptome-Wide Characterization of the MADS-Box Family in Pinesap Monotropa hypopitys Reveals Flowering Conservation in Non-photosynthetic Myco-Heterotrophs

Pinesap Monotropa hypopitys is a myco-heterotrophic non-photosynthetic higher angiosperm perennial plant devoid of vegetative organs and with standard flower arrangement. The MADS-domain transcription factor family has multiple regulatory functions in plant life cycle and is implicated in flower evolution and diversity. This study is the first to describe the MADS-box genes in a myco-heterotrophic eudicot. By performing the M. hypopitys transcriptome-wide analysis, we identified 30 MADS-box genes belonging to the major clades in the MIKCc and MIKC* lineages. Among them, MhyMADS18 is suggested as an ancestral gene of the cluster comprising AP1/FUL, FLC, SEP, and AGL6 clades. The RNA-seq profiling of the MhyMADS expression in the flowering plant revealed mRNAs specific to bracts, flowers, and roots with adventitious buds. Our results represent systematic and expression analysis of the pinesap MADS-box genes that may be involved in seed dormancy regulation, flowering time control, and flower organ identity specification. The obtained data should further our understanding of the roles played by the MADS-box genes in developmental regulation of myco-heterotrophic plants.