Analysis of the floral transcriptome uncovers new regulators of organ determination and gene families related to flower organ differentiation in Gerbera hybrida (Asteraceae)

Abstract

Development of composite inflorescences in the plant family Asteraceae has features that cannot be studied in the traditional model plants for flower development. In Gerbera hybrida, inflorescences are composed of morphologically different types of flowers tightly packed into a flower head (capitulum). Individual floral organs such as pappus bristles (sepals) are developmentally specialized, stamens are aborted in marginal flowers, petals and anthers are fused structures, and ovaries are located inferior to other floral organs. These specific features have made gerbera a rewarding target of comparative studies. Here we report the analysis of a gerbera EST database containing 16,994 cDNA sequences. Comparison of the sequences with all plant peptide sequences revealed 1656 unique sequences for gerbera not identified elsewhere within the plant kingdom. Based on the EST database, we constructed a cDNA microarray containing 9000 probes and have utilized it in identification of flower-specific genes and abundantly expressed marker genes for flower scape, pappus, stamen, and petal development. Our analysis revealed several regulatory genes with putative functions in flower-organ development. We were also able to associate a number of abundantly and specifically expressed genes with flower-organ differentiation. Gerbera is an outcrossing species, for which genetic approaches to gene discovery are not readily amenable. However, reverse genetics with the help of gene transfer has been very informative. We demonstrate here the usability of the gerbera microarray as a reliable new tool for identifying novel genes related to specific biological questions and for large-scale gene expression analysis.

Figure 1.

ESTs encoding non-specific lipid transfer proteins are the most abundant transcripts during late petal development in gerbera. Gene mining of the gerbera EST database revealed a gene family composed of at least ten LTP genes. (A) Sequence similarity comparison between the gerbera LTPs based on amino acid similarity (%) of the consensus sequences retrieved from gerbera LTP clusters indicate that the cDNAs are encoding different gene family members. GLTP1 represents the previously isolated gerbera gene [X31588] and corresponds to C_G0000300001A01. (B) Expression analysis of the gerbera LTP genes detected in the microarray comparison of various flower organs reveals several tissue specifically expressed gene family members. The probe for GLTP1 corresponds to C_G0000300001A01. Cluster C_G0000500007B05 is represented by the EST G0000700011D11 on the microarray.