Identification of a novel compound that inhibits both mitochondria-mediated necrosis and apoptosis.

In various pathological events, particularly in oxygen radical-mediated cell injury, both apoptosis and necrosis play essential roles. Apoptosis and some types of necrosis are induced via increases in mitochondrial membrane permeability, called mitochondrial outer membrane permeabilization (MOMP) and permeability transition pore (PTP) opening, respectively. To search for small compounds that inhibit both MOMP-mediated apoptosis and PTP-mediated necrosis, we performed a mitochondria-based high-throughput screening of a chemical library. We identified TMD#7538, a small compound that inhibits both MOMP and PTP opening. Consistent with the fact that this compound inhibited both apoptosis and necrosis, it efficiently suppressed H2O2-induced cell death in mouse embryonic fibroblasts and rat neonatal cardiomyocytes.

Non-cell-autonomous control of vascular stem cell fate by a CLE peptide/receptor system.

Land plants evolved a long-distance transport system of water and nutrients composed of the xylem and phloem, both of which are generated from the procambium- and cambium-comprising vascular stem cells. However, little is known about the molecular mechanism of cell communication governing xylem-phloem patterning. Here, we show that a dodecapeptide (HEVHypSGHypNPISN; Hyp, 4-hydroxyproline), TDIF (tracheary element differentiation inhibitory factor), is secreted from the phloem and suppresses the differentiation of vascular stem cells into xylem cells through a leucine-rich repeat receptor-like kinase (LRR-RLK). TDIF binds in vitro specifically to the LRR-RLK, designated TDR (putative TDIF receptor), whose expression is restricted to procambial cells. However, the combined analysis of TDIF with a specific antibody and the expression profiles of the promoters of two genes encoding TDIF revealed that TDIF is synthesized mainly in, and secreted from, the phloem and its neighboring cells. The observation that TDIF is capable of promoting proliferation of procambial cells while suppressing xylem differentiation suggests that this small peptide functions as a phloem-derived, non-cell-autonomous signal that controls stem cell fate in the procambium. Our results indicate that we have discovered a cell communication system governing phloem-xylem cross-talk.

Dodeca-CLE peptides as suppressors of plant stem cell differentiation.

In plants and animals, small peptide ligands that signal in cell-cell communication have been suggested to be a crucial component of development. A bioassay of single-cell transdifferentation demonstrates that a dodecapeptide with two hydroxyproline residues is the functional product of genes from the CLE family, which includes CLAVATA3 in Arabidopsis. The dodecapeptide suppresses xylem cell development at a concentration of 10(-11) M and promotes cell division. An application, corresponding to all 26 Arabidopsis CLE protein family members, of synthetic dodecapeptides reveals two counteracting signaling pathways involved in stem cell fate.

CLV3/ESR-related (CLE) peptides as intercellular signaling molecules in plants.

For many years, the plant hormones auxin, cytokinin, ethylene, gibberellin, abscisic acid, brassinosteroid, jasmonic acid, and salicylic acid have been extensively studied as key regulators of plant growth and development. However, recent biochemical and genetic analyses have revealed that secretory peptides are also responsible for intercellular signaling in plants and regulate various events including wound response, cell division control, and pollen self-incompatibility. We discovered two natural CLAVATA3 (CLV3)/ESR-related (CLE) peptides: tracheary elements differentiation inhibitory factor (TDIF) and CLV3, which are dodecapeptides with two hydroxyproline residues that regulate vascular development and meristem formation, respectively. This discovery enabled us to predict the chemical form of CLE gene products. In the Arabidopsis genome, there are 31 CLE genes that correspond to 26 CLE peptides. The application of all 26 chemically synthesized peptides to plants revealed the existence of distinctive functional groups. From these results, we discuss the functions of CLE peptides in plant development and plant-parasite interactions.

Preferential and asymmetrical accumulation of a Rac small GTPase mRNA in differentiating xylem cells of Zinnia elegans.

Rac-type small GTPases are known to function in some cellular processes in plants. To further understand the involvement of Rac type GTPases in plant development, we isolated from cultured Zinnia cells a gene (ZeRAC2) encoding a new Rac-type small GTPase. ZeRAC2 mRNA accumulates preferentially in xylogenic culture and transiently at the time when visible tracheary elements appear. Experiments with ZeRAC2 recombinant proteins demonstrated that ZeRAC2 binds to and hydrolyzes GTP. A GFP-ZeRAC2 fusion protein was localized to the plasma membrane. Together with the fact that ZeRAC2 possesses a putative geranylgeranylation site at the C-terminus, this suggests that ZeRAC2 acts on the plasma membrane. In situ hybridization indicated that ZeRAC2 mRNA accumulates preferentially in xylem parenchyma and tracheary element precursor cells, and surprisingly the accumulation is restricted to the site facing developing tracheary elements.