SCI1 e NtCDKG;2 atuam no ciclo celular, no processamento de RNAs e no desenvolvimento floral em Nicotiana tabacum

Abstract

Flower development is a complex process which depends on the fine-tuned coordination of organ identity establishment, cell proliferation, differentiation, and expansion. If this process occurs successfully, a flower is produced, and this Angiosperms reproductive structure is essential for the plant life cycle. One of the genes that participates in flower development is SCI1 (Stigma/style Cell cycle Inhibitor 1). This gene is expressed since the formation of the floral meristem, and disturbances in its expression were able to alter the final size of the pistil, more specifically, of the stigmas and styles. These size changes occurred due to changes in cell proliferation during pistil development. Regarding the mechanism by which SCI1 affects cell proliferation, it is proposed that it inhibits CDK-cyclin complexes, which are important components of cell cycle control. One of the targets of SCI1 is the NtCDKG;2, a CDK possibly involved in the mitotic spindle assembly. To better understand the molecular network by which SCI1 acts during flower development, an RNA-seq strategy was employed. With this approach, differential gene expression was detected in stigmas/styles of transgenic plants silencing the SCI1 gene, compared to the wild type. Among the 1,510 differentially expressed (DE) genes, 72.8%% are downregulated when SCI1 is silenced. Functional classification of the DE genes revealed that 84 of them are connected to the cell cycle, 39 are auxin responsive genes, 99 are involved in flower development, and 47 are related to RNA processing. Of the cell cycle genes, 46% have greater expression in the S and G2 phases of the cycle, which indicates a relevance of SCI1 in these phases. In addition, the differential expression of alternative transcripts of the NtSR30 gene, which encodes a splicing regulatory protein, was detected. In previous studies, SCI1 was associated with splicing due to its interacting partner proteins. The results of this work contribute to the hypothesis of the participation of SCI1 in this process. Additionally, NtCDKG;2 also has interaction partners involved in splicing, such as NtCycL1 and NtRSZ21. According to analyzes of amino acid sequences, in this work it was clarified that NtCDKG;2 is homologous to CDKG;2 of Arabidopsis thaliana and CDK11 of Homo sapiens, both with roles described in splicing. In addition, phylogenetic analyzes of plant CDKGs suggest that this CDK has a deep origin in the phylogeny of green plants, which demonstrates its importance for these species. Additionally, it was verified that the protein NtCDKG;2 has isoforms present in tissue-specific form in vegetative and reproductive organs. Interestingly, in an analysis of the seed size in transgenic plants of overexpression and silencing of the NtCDKG;2 gene, it was possible to detect differences that indicate the participation of this gene in the development of these organs. In short, this work was able to identify the possible molecular pathways in which SCI1 participates during floral development. Furthermore, its import...