Abstract
Cleistogenes songorica, a grass species that exhibits two spatially different type of inflorescence, chastogamy (CH), flowers localized at the top, and cleistogamy (CL) flowers embedded in leaf sheath. This study aimed at dissecting reasons underlying these distinct floral development patterns at morphological and microRNA level. Phenotyping for CH and CL was conducted and four small RNA libraries were constructed from the CH and CL flowers for high-throughput sequencing to identify the differentiated miRNAs. As results, spikelet, stigma, anther, lemma and lodicule length of CH flowers were found larger than that of CL, and so was seed setting. Also, 17 flower-related differential expression miRNAs were identified which were associated with floral organ development and morphogenesis, and the flower development. Further results showed that miR159a.1-CL3996.Contig2 pair was related to anther development, miR156a-5p-CL1954.Contig2 was linked to response to high light intensity, miR408-3p/miR408d-Unigene429 was related to pollination and Unigene429 positively regulated flower development. To our knowledge, this is the first study on differential miRNA accumulation between CH and CL flowers and our study serves as a foundation to the future elucidation of regulatory mechanisms of miRNAs in the divergent development of CL and CH flowers in a single plant.
Highlights
Chasmogamy (CH), an open-pollinated reproduction mechanism, is typical in grasses, with open flowers where the palea and the lemma are compelled separation exposing the pistil to disperse anemophilous pollen[1]
To study the drought mechanism of C. songorica, leaf and root Expression Sequence Tag (EST) resources have been used to investigate drought stress-responsive genes[13], and some genes were transformed into Arabidopsis thaliana and alfalfa to confirm and enhance the stress tolerance[14,15,16,17]
A previous study indicated that CL phenotype of barley and rice was caused by lack lodicules or defect lodicules, the reason for this condition is due to the mutation of floral development related genes, like Cleistogamy (Cly1). miRNA172 causes the down-regulation of barley Cly[1], as a result lodicules growth is restrained, and CL is induced[7]
Summary
Chasmogamy (CH), an open-pollinated reproduction mechanism, is typical in grasses, with open flowers where the palea and the lemma are compelled separation exposing the pistil to disperse anemophilous pollen[1]. Through regulating the genes expression, miRNAs, as important regulators, control plant growing and developing, in this way to encode transcription factors and regulatory proteins[21,22]. Even though the differential gene expression patterns of natural dimorphic cleistogamy plants have been studied in Pseudostellaria heterophylla[10] and Viola philippica[12], the miRNAs involved in flower development of dimorphic plant remains unknown. The aims of this study include (1) to report the morphological differences of CH and CL in seeds, florets, lodicules and pollen grains; (2) to characterize miRNAs in CH and CL flowers and provide platform for further investigation of specific miRNAs in various biological processes; (3) to investigate the miRNAs and targets interaction in order to illuminate the potential miRNA-mediated regulatory mechanism on chasmogamy and cleistogamy in C. songorica. The differential accumulation of miRNA between CH and CL flowers will provide novel insights into the development of dimorphism and the molecular basis of drought resistance
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