ABA Represses the Expression of Cell Cycle Genes and May Modulate the Development of Endodormancy in Grapevine Buds.

Recently, the plant hormone abscisic acid (ABA) has been implicated as a key player in the regulation of endodormancy (ED) in grapevine buds (Vitis vinifera L). In this study, we show that in the vine, the expression of genes related to the biosynthesis of ABA (VvNCED1; VvNCED2) and the content of ABA are significantly higher in the latent bud than at the shoot apex, while the expression of an ABA catabolic gene (VvA8H3) showed no significant difference between either organ. A negative correlation between the content of ABA and transcript levels of cell cycle genes (CCG) was found in both tissues. This result suggested that ABA may negatively regulate the expression of CCG in meristematic tissues of grapevines. To test this proposition, the effect of ABA on the expression of CCG was analyzed in two meristematic tissues of the vine: somatic embryos and shoot apexes. The results indicated that cell cycle progression is repressed by ABA in both organs, since it down-regulated the expression of genes encoding cyclin-dependent kinases (VvCDKB1, VvCDKB2) and genes encoding cyclins of type A (VvCYCA1, VvCYCA2, VvCYCA3), B (VvCYCB), and D (VvCYCD3.2a) and up-regulated the expression of VvICK5, a gene encoding an inhibitor of CDKs. During ED, the content of ABA increased, and the expression of CCG decreased. Moreover, the dormancy-breaking compound hydrogen cyanamide (HC) reduced the content of ABA and up-regulated the expression of CCG, this last effect was abolished when HC and ABA were co-applied. Taken together, these results suggest that ABA-mediated repression of CCG transcription may be part of the mechanism through which ABA modulates the development of ED in grapevine buds.

Cell cycle genes are activated earlier than respiratory genes during release of grapevine buds from endodormancy.

Single-bud cuttings of Vitis vinifera L exposed to forced growing conditions were used to investigate the involvement of phytohormones, abscisic acid (ABA), auxin (Aux) and cytokinin (CK) in the release of buds from the ED and in bud-sprouting. This artificial system imitates and hastens the natural sprouting that occurs in spring. Temporal expression analysis of genes related to phytohormones synthesis, showed an early drop in the expression of ABA biosynthesis gene that preceded an increase in Aux and CK biosynthesis genes. Bud-break is headed by the activation of all structures of the latent bud, especially the differentiation of the inflorescence and the development of the early stages of floral organs. Therefore, resumption of cell division and increases in respiration are essential for the activation of the bud. Temporal expression analysis of the cell cycle and respiration genes indicate that an increase in cell division go before the increase in respiration. These results, together with results indicating that the cell cycle genes are upregulated by Aux and CK, suggest that the events before the bud-break, start with a reduction in ABA content, followed by an increase in the content of Aux and CK, which activates the machinery of the cell cycle, which eventually would cause an increase in respiration.

Cohesin subunits, STAG1 and STAG2, and cohesin regulatory factor, PDS5b, in oral squamous cells carcinomas.

BACKGROUND: Cohesin complex is responsible for sister chromatid cohesion. STAG1/STAG2 is part of the complex, which is regulated by PDS5B. Alterations in these genes were described in tumors. PDS5B is a negative regulator of cell proliferation. We aimed to assess molecular alterations in these genes in oral squamous cell carcinoma (OSCC) and predict their expression by the expression of 84 cell cycle genes. In addition, we investigated whether pds5b protein expression impacted ki-67 and p53 immunopositivity. METHODS: We assessed loss of heterozygosity (LOH) at STAG1 and STAG2 loci in 15 OSCC using three polymorphic markers. Associations between the immunoexpression of pds5b and ki-67 and p53 were tested in 62 samples. Differences between transcriptional levels of STAG1, STAG2, and PDS5B between OSCC and normal oral mucosa (NM) were evaluated by qPCR. An 84 cell cycle genes qPCR array was carried with OSCC samples, and STAG1, STAG2, and PDS5B were independently used as response variables in multiple linear regression models. RESULTS: Loss of heterozygosity in at least one marker was observed in three samples. pds5b, p53, and ki-67 were highly expressed, and no association was found between pds5b immunoexpression and ki-67 or p53 (P > 0.05). OSCC and NM showed similar transcriptional levels of STAG1, STAG2, and PDS5B. STAG1 and CUL3 expression seem to be related (P = 0.004). CONCLUSIONS: There is LOH at STAG1 and STAG2 loci in OSCC, but OSCC and NM showed similar transcriptional levels of STAG1, STAG2, and PDS5B. pds5b immunoexpression in OSCC was high, but it was not associated with proliferation cell index.