Salicylic Acid Targets Protein Phosphatase 2A to Attenuate Growth in Plants.

Plants, like other multicellular organisms, survive through a delicate balance between growth and defense against pathogens. Salicylic acid (SA) is a major defense signal in plants, and the perception mechanism as well as downstream signaling activating the immune response are known. Here, we identify a parallel SA signaling that mediates growth attenuation. SA directly binds to A subunits of protein phosphatase 2A (PP2A), inhibiting activity of this complex. Among PP2A targets, the PIN2 auxin transporter is hyperphosphorylated in response to SA, leading to changed activity of this important growth regulator. Accordingly, auxin transport and auxin-mediated root development, including growth, gravitropic response, and lateral root organogenesis, are inhibited. This study reveals how SA, besides activating immunity, concomitantly attenuates growth through crosstalk with the auxin distribution network. Further analysis of this dual role of SA and characterization of additional SA-regulated PP2A targets will provide further insights into mechanisms maintaining a balance between growth and defense.

Synthesis, Bacteriostatic and Anticancer Activity of Novel Phenanthridines Structurally Similar to Benzo[c]phenanthridine Alkaloids.

In this study, we report the synthesis, antibacterial and anticancer evaluation of 38 novel phenanthridines that were designed as analogs of the benzo[c]phenanthridine alkaloids. The prepared phenanthridines differ from the benzo[c]phenanthridines in the absence of a benzene A-ring. All novel compounds were prepared from 6-bromo-2-hydroxy-3-methoxybenzaldehyde in several synthetic steps through reduction of Schiff bases and accomplished by radical cyclization. Twelve derivatives showed high antibacterial activity against Bacillussubtilis, Micrococcusluteus and/or Mycobacteriumvaccae at single digit micromolar concentrations. Some compounds also displayed cytotoxicity against the K-562 and MCF-7 cancer cell lines at as low as single digit micromolar concentrations and were more potent than chelerythrine and sanguinarine. The active compounds caused cell-cycle arrest in cancer cells, increased levels of p53 protein and caused apoptosis-specific fragmentation of PARP-1. Biological activity was connected especially with the presence of the N-methyl quaternary nitrogen and 7-benzyloxy substitution (compounds 7i, 7j, 7k, and 7l) of phenanthridine.