Genome-wide comparison of strigolactones signaling genes in Orchidaceae and functional characterization of PaD14s in Phalaenopsis aphrodite subsp formosana

Abstract

Phalaenopsis orchids have become globally popular for their long-lasting flowers with elegant floral morphology and various flower colors Taiwan is one of the major exporting countries of Phalaenopsis taking an important role in economic crops With molecular biology technology we can have insights into Phalaenopsis genome which can promote the development of floricultural industry Strigolactones (SLs) as a family of carotenoid-derived phytohormone are recently recognized as endogenous plant signaling compounds SL signal transduction mechanisms employ ?/β-hydrolase-derived receptors (D14) that confer E3 ubiquitin ligase-mediated protein (D3) degradation processes which lead transcription factor repressor protein (D53) degradation SLs play important roles in plant development including inhibiting plant axillary branching inducing parasitic interactions and various plant stress responses After SLs released in the rhizosphere SLs would be able to attract mycorrhizal fungi to symbiosis with host plants This SL function is especially important for orchid because orchids seed depends on symbiotic fungi to obtain enough carbon source and grow properly In addition SLs can also affect the axillary branching number If orchids can increase branch numbers by manipulating SLs I believe orchids will be much more popular However there are seldom researches studying the roles of SL in Phalaenopsis In this study we detected two different SLs in Phalaenopsis orchid by LC-MS/MS Based on the sequenced orchid genome database we identified two SL receptor genes in all detected orchids and named SL receptor genes in Phalaenopsis aphrodite as PaD14-1 and PaD14-2 There is one transcription factor repressor gene in every detected orchid genome except Vanilla containing two repressor genes We named the repressor gene in P aphordite as PaD53 There is one F-box protein in tested orchid genomes except two in Platanthera zijinensis By qRT-PCR analysis we found that PaD14-1 expression was obviously higher than PaD14-2 in all detected P aphordite tissues and that all SL signaling related genes in P aphordite had higher expression level in vegetative tissues than in reproductive tissues This result might illustrate to that SLs function mainly affect in vegetative tissue development With yeast two hybrid (Y2H) assay and bimolecular fluorescence complementation (BiFC) assay identification of the interaction between ?/β hydrolase PaD14s and repressor protein PaD53 was proven in P aphrodite in the presence of exogenously applied GR24 a synthetic SL analog Functional analysis was performed by overexpression of PaD14-1 gene in Arabidopsis The Arabidopsis PaD14-1OE plants displayed a similar phenotype to the wild-type Col-0 with only slightly increased leaf numbers and obviously shortened the length of seedling primary roots and lateral root Based on this thesis results SL was confirmed the existence in P aphrodite and PaD14-1 is confirmed as one of the functional SL receptor genes

Date of Award	2020
Original language	English
Supervisor	Wen-Chieh Tsai (Supervisor)