Exploiting genomics for the promoters of B-class floral organ identity genes and the transcription factors regulating flower color in Phalaenopsis orchids

Abstract

Phalaenopsis orchids have become very popular for their long-lasting flowers with elegant floral morphology and various flower colors Development of new cultivars is economically important for floricultural industry worldwide This thesis contains two parts: (1) analysis of the genome structure and composition and (2) study of the regulatory mechanism for the promoters of B-class floral organ identity genes and the transcription factors regulating flower color in Phalaenopsis For the first part pair-end sequences from 2 920 bacterial artificial chromosome (BAC) clones of P equestris were analyzed for the compositions of protein-coding regions repeat sequences and microsatellites in the P equestris genome The LTR-retrotransposons were identified from the BAC end sequences (BESs) and partial genome sequences and examined for their retrotransposition/recombination events and effects on Phalaenopsis genome sizes Their copy numbers were assessed in the genome sequences of four Phalaenopsis species with either small or large chromosomes For the second part of studying the regulation of orchid morphogenesis the promoter sequences of five B-class MADS-box genes (PeMADS2~6) were identified and analyzed These included four APETALA3 (AP3)-like PeMADS2~5 and one PISTILLATA (PI)-like PeMADS6 displaying distinct expression profiles in various floral organs and specifying the spectacular flower morphology in orchids Further studies on DNA methylation and histone modification status of PeMADS2~6 were performed The regulation via the upstream sequences as well as increased histone acetylation levels may involve in the distinct expression profiles of the AP3-like genes for Phalaenopsis floral morphogenesis To investigate the floral pigmentation patterning genome-wide identification of regulatory genes involved in the flower color and anthocyanin biosynthesis pathway in Phalaenopsis such as MYBs was performed Three R2R3-MYB transcription factors PeMYB2 PeMYB11 and PeMYB12 were characterized for their roles in regulating three distinct floral pigmentation patterns full-red red-spot and venation patterns respectively in one single flower of Phalaenopsis In addition various ratios of these three PeMYBs were concomitant with distinct floral pigmentation patterns in six commercial cultivars These results unravel the complicated regulation of anthocyanin pigmentation patterning in Phalaenopsis which leads to the highly abundant color patterns in orchid flowers All these results together improve our knowledge on the genome composition and the regulation of floral morphogenesis and pigmentation patterning in Phalaenopsis orchids through genomics approach

Date of Award	2014 Dec 2
Original language	English
Supervisor	Hong-Hwa Chen (Supervisor)