Synthesis, biological evaluation and preliminary mechanisms of 6-amino substituted harmine derivatives as potential antitumor agents.

To explore the effect of the introduction of the amino and substituted amino groups on the antitumor activity of harmine, twenty-five novel 6-amino substituted harmine derivatives (3a-3j and 5a-5o) were synthesized and evaluated for anti-proliferative activity on a panel of cancer cell lines. Compounds 3i and 5n exhibited the most potent antiproliferative activity with IC50 values lower than 2.2 µM. Especially, compound 5n possessed extremely potent antitumor activity with IC50 values of 0.34 µM and 0.65 µM against HL-60 and A549 cell lines, respectively. Further, the preliminary studies of mechanisms showed that compound 5n could significantly induce cell apoptosis in a dose-dependent manner, cause cell cycle arrest at the G2/M phase and intercalate into ct-DNA via the competition with EB, while displaying very weak topoisomerase I (Topo I) inhibition activity. More importantly, 5n showed mild cytotoxicity against human normal lung epithelial cells BEAS-2B. Based on these considerations, 5n may be a good antitumor candidate compound for further exploration.

TINY BRANCHED HAIR functions in multicellular trichome development through an ethylene pathway in Cucumis sativus L.

The fruit trichomes of Cucurbitaceae are widely desired in many Asian countries and have been a key determinant of cucumber (Cucumis sativus L.) cultivar selection for commercial production and breeding. However, our understanding of the initiation and development of cucumber trichomes is still limited. Here, we found that the cucumber TINY BRANCHED HAIR (TBH) gene is preferentially expressed in multicellular trichomes. Overexpression of CsTBH in tbh mutants restored the trichome phenotype and increased the percentage of female flowers, whereas silencing of CsTBH in wild-type plants resulted in stunted trichomes with a lower rate of female flowers. Furthermore, we provide evidence that CsTBH can directly bind to the promoters of cucumber 1-Aminocyclopropane-1-Carboxylate Synthase (CsACS) genes and regulate their expression, which affects multicellular trichome development, ethylene accumulation, and sex expression. Two cucumber acs mutants with different trichome morphology and sex morphs compared with their near-isogenic line further support our findings. Collectively, our study provides new information on the molecular mechanism of CsTBH in regulating multicellular trichome development and sex expression through an ethylene pathway.

A GAMYB homologue CsGAMYB1 regulates sex expression of cucumber via an ethylene-independent pathway.

Cucumber (Cucumis sativus L.) is a typical monoecious vegetable with individual male and female flowers, and has been used as a model plant for sex determination. It is well known that sex differentiation of cucumber can be regulated by phytohormones, such as gibberellic acid (GA) and ethylene. The molecular mechanism of female sex expression modulated by ethylene has been widely understood, but how GA controls male sex expression remains elusive. In hermaphroditic Arabidopsis and rice, GA can regulate stamen and anther development via the transcriptional regulation of GAMYB. Here we characterized a GAMYB homologue CsGAMYB1 in cucumber. We found that CsGAMYB1 is predominantly expressed in male flower buds, where its expression is upregulated by GA3 treatment. CsGAMYB1 protein is localized in the nucleus. CsGAMYB1 can partially rescue stamen development and fertility phenotypes of an Arabidopsis myb33 myb65 double mutant. However, constitutive overexpression of CsGAMYB1 in wild-type Arabidopsis resulted in male sterility, which mimics the effect of GA overdose in flower development. Knockdown of CsGAMYB1 in cucumber decreases the ratio of nodes with male and female flowers, and ethylene is not involved in this process. Our data suggest that CsGAMYB1 regulates sex expression of cucumber via an ethylene-independent pathway.