Plant-specific calreticulin is localized in the nuclei of highly specialized cells in the pistil-new observations for an old hypothesis.

One of the first cellular locations of the calreticulin (CRT) chaperone in eukaryotic cells, apart from its obvious localization in the endoplasmic reticulum (ER), was the cell nucleus (Opas et al. 1991). The presence of CRT has been detected inside the nucleus and in the nuclear envelope of animal and plant cells, and a putative nuclear localization signal (NLS) in the CRT amino acid sequence has been mapped in several animal and plant species.

RNAi-Mediated Knockdown of Calreticulin3a Impairs Pollen Tube Growth in .

Pollen tube growth depends on several complex processes, including exo/endocytosis, cell wall biogenesis, intracellular transport, and cell signaling. Our previous results provided evidence that calreticulin (CRT)-a prominent calcium (Ca)-buffering molecular chaperone in the endoplasmic reticulum (ER) lumen-is involved in pollen tube formation and function. We previously cloned and characterized the gene belonging to the 2 subgroup from (), and found that post-transcriptional silencing of expression strongly impaired pollen tube growth in vitro.

Calreticulin expression and localization in relation to exchangeable Ca during pollen development in Petunia.

Background: Pollen development in the anther in angiosperms depends on complicated cellular interactions associated with the expression of gametophytic and sporophytic genes which control fundamental processes during microsporo/gametogenesis, such as exo/endocytosis, intracellular transport, cell signaling, chromatin remodeling, and cell division. Most if not all of these cellular processes depend of local concentration of calcium ions (Ca). Work from our laboratory and others provide evidence that calreticulin (CRT), a prominent Ca-binding/buffering protein in the endoplasmic reticulum (ER) of eukaryotic cells, may be involved in pollen formation and function.

Mutations Q93H and E97K in Disrupt Ca-Dependent Regulation of Actin Filaments.

Tropomyosin is a two-chain coiled coil protein, which together with the troponin complex controls interactions of actin with myosin in a Ca-dependent manner. In fast skeletal muscle, the contractile actin filaments are regulated by tropomyosin isoforms Tpm1.1 and Tpm2.

Phylogenetic analysis of plant calreticulin homologs.

Calreticulin (CRT) is an multifunctional resident endoplasmic reticulum (ER) luminal protein implicated in regulating a variety of cellular processes, including Ca storage/mobilization and protein folding. These multiple functions may be carried out by different CRT genes and protein isoforms. The plant CRT family consist of three genes: CRT1 and CRT2 classified in the common subclass (CRT1/2), and CRT3.

Calreticulin localizes to plant intra/extracellular peripheries of highly specialized cells involved in pollen-pistil interactions.

Calcium (Ca) plays essential roles in generative reproduction of angiosperms, but the sites and mechanisms of Ca storage and mobilization during pollen-pistil interactions have not been fully defined. Both external and internal Ca stores are likely important during male gametophyte communication with the sporophytic and gametophytic cells within the pistil. Given that calreticulin (CRT), a Ca-buffering protein, is able to bind Ca reversibly, it can serve as a mobile store of easily releasable Ca (so called an exchangeable Ca) in eukaryotic cells.

Calreticulin is required for calcium homeostasis and proper pollen tube tip growth in Petunia.

Calreticulin is involved in stabilization of the tip-focused Ca gradient and the actin cytoskeleton arrangement and function that is required for several key processes driving Petunia pollen tube tip growth. Although the precise mechanism is unclear, stabilization of a tip-focused calcium (Ca) gradient seems to be critical for pollen germination and pollen tube growth. We hypothesize that calreticulin (CRT), a Ca-binding/buffering chaperone typically residing in the lumen of the endoplasmic reticulum (ER) of eukaryotic cells, is an excellent candidate to fulfill this role.

Nuclear matrix - structure, function and pathogenesis.

The nuclear matrix (NM), or nuclear skeleton, is the non-chromatin, ribonucleoproteinaceous framework that is resistant to high ionic strength buffers, nonionic detergents, and nucleolytic enzymes. The NM fulfills a structural role in eukaryotic cells and is responsible for maintaining the shape of the nucleus and the spatial organization of chromatin. Moreover, the NM participates in several cellular processes, such as DNA replication/repair, gene expression, RNA transport, cell signaling and differentiation, cell cycle regulation, apoptosis and carcinogenesis.