Comparative analysis of pistil transcriptomes reveals conserved and novel genes expressed in dry, wet and semi-dry stigmas

摘要

Fertilization in angiosperms depends on a complex cellular "courtship" between haploid pollen and diploid pistil. These pollen-pistil interactions are regulated by a diversity of molecules, many of which remain to be identified and characterized. Thus it is unclear to what extent these processes are conserved among angiosperms, a fact confounded by limited sampling across taxa. Here we report analysis of pistil-expressed genes in Senecio squalidus (Asteraceae), a species from euasterid II, a major clade for which there is currently no data on pistil-expressed genes. Species from the Asteraceae typically have a "semi-dry stigma", intermediate between the "wet" and "dry" stigmas typical of the majority of angiosperms. Construction of pistil-enriched cDNA libraries for S. squalidus allowed us to address two hypotheses: i) stigmas of S. squalidus will express genes common to wet and dry stigmas and genes specific to the semi-dry stigma characteristic of the Asteraceae, and ii) genes potentially essential for pistil function will be conserved between diverse angiosperm groups and therefore common to all currently available pistil transcriptome data sets, including Senecio. Our data support both these hypotheses: The S. squalidus pistil transcriptome contains novel genes and genes previously identified in pistils of species with dry stigmas and wet stigmas. Comparative analysis of the five pistil transcriptomes currently available (Oryza sativa, Crocus sativus, Arabidopsis thaliana, Nicotiana tabacum, and Senecio squalidus), representing four major angiosperm clades and the three stigma states, identified novel genes and conserved genes potentially regulating pollen-pistil interaction pathways common to monocots and eudicots.