Abstract
BackgroundIn flowering plants a number of genes have been identified which control the transition from a vegetative to generative phase of life cycle. In bryophytes representing basal lineage of land plants, there is little data regarding the mechanisms that control this transition. Two species from bryophytes - moss Physcomitrella patens and liverwort Marchantia polymorpha are under advanced molecular and genetic research. The goal of our study was to identify genes connected to female gametophyte development and archegonia production in the dioecious liverwort Pellia endiviifolia species B, which is representative of the most basal lineage of the simple thalloid liverworts.ResultsThe utility of the RDA-cDNA technique allowed us to identify three genes specifically expressed in the female individuals of P.endiviifolia: PenB_CYSP coding for cysteine protease, PenB_MT2 and PenB_MT3 coding for Mysterious Transcripts1 and 2 containing ORFs of 143 and 177 amino acid residues in length, respectively. The exon-intron structure of all three genes has been characterized and pre-mRNA processing was investigated. Interestingly, five mRNA isoforms are produced from the PenB_MT2 gene, which result from alternative splicing within the second and third exon. All observed splicing events take place within the 5′UTR and do not interfere with the coding sequence. All three genes are exclusively expressed in the female individuals, regardless of whether they were cultured in vitro or were collected from a natural habitat. Moreover we observed ten-fold increased transcripts level for all three genes in the archegonial tissue in comparison to the vegetative parts of the same female thalli grown in natural habitat suggesting their connection to archegonia development.ConclusionsWe have identified three genes which are specifically expressed in P.endiviifolia sp B female gametophytes. Moreover, their expression is connected to the female sex-organ differentiation and is developmentally regulated. The contribution of the identified genes may be crucial for successful liverwort sexual reproduction.
Highlights
In flowering plants a number of genes have been identified which control the transition from a vegetative to generative phase of life cycle
The utility of the technique RDA-cDNA allowed us to identify three genes expressed in the female individuals of P.endiviifolia
Isolation of cDNA fragments of genes expressed in the female P.endiviifolia sp B gametophytes using RDA-cDNA approach The RDA-cDNA technique was employed for dioecious liverwort P.endiviifolia sp B to identify genes involved in the female thalli and archegonia development. cDNAs obtained from the liverwort thalli collected from the natural environment during two seasons (2006 and 2007) were used in four rounds of subtractive hybridization. cDNA obtained from RNA isolated from the female gametophytes producing archegonia was used as the TESTER and cDNA obtained from RNA isolated from the male gametophytes producing antheridia as the DRIVER
Summary
In flowering plants a number of genes have been identified which control the transition from a vegetative to generative phase of life cycle. The gametophytes of lower plants, such as the bryophytes, are free living organisms that undergo differentiation and development independent of the sporophytes, whereas the gametophytes of flowering plants complete their development within the floral organs of the sporophytes [1] In flowering plants such as Arabidopsis thaliana, the transition from the sporophytic phase to the gametophytic phase consists of two sequential processes, sporogenesis and gametogenesis. In the basal lineage of land plants, bryophytes, moss Physcomitrella patens has emerged as a model organism for molecular studies to learn about the mechanisms controlling the key moments during the transition from vegetative to reproductive phase of its life cycle. A critical role of moss 2 KNOTTED LIKE HOMEOBOX (KNOX2) transcription factors was demonstrated in preventing the development of gametophyte leafy shoots from diploid embryos before meiosis [9] indicating a critical role for the evolution of KNOX2 in establishing an alternation of generation in land plants
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