Dataset Information

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

ABSTRACT: Calreticulin is involved in stabilization of the tip-focused Ca 2+ 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 (Ca2+) gradient seems to be critical for pollen germination and pollen tube growth. We hypothesize that calreticulin (CRT), a Ca2+-binding/buffering chaperone typically residing in the lumen of the endoplasmic reticulum (ER) of eukaryotic cells, is an excellent candidate to fulfill this role. We previously showed that in Petunia pollen tubes growing in vitro, CRT is translated on ER membrane-bound ribosomes that are abundant in the subapical zone of the tube, where CRT's Ca2+-buffering and chaperone activities might be particularly required. Here, we sought to determine the function of CRT using small interfering RNA (siRNA) to, for the first time in pollen tubes growing in vitro, knockdown expression of a gene. We demonstrate that siRNA-mediated post-transcriptional silencing of Petunia hybrida CRT gene (PhCRT) expression strongly impairs pollen tube growth, cytoplasmic zonation, actin cytoskeleton organization, and the tip-focused Ca2+ gradient. Moreover, reduction of CRT alters the localization and disturbs the structure of the ER in abnormally elongating pollen tubes. Finally, cytoplasmic streaming is inhibited, and most of the pollen tubes rupture. Our data clearly show an interplay between CRT, Ca2+ gradient, actin-dependent cytoplasmic streaming, organelle positioning, and vesicle trafficking during pollen tube elongation. Thus, we suggest that CRT functions in Petunia pollen tube growth by stabilizing Ca2+ homeostasis and acting as a chaperone to assure quality control of glycoproteins passing through the ER.

SUBMITTER: Suwinska A

PROVIDER: S-EPMC5391374 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

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

Suwińska Anna A Wasąg Piotr P Zakrzewski Przemysław P Lenartowska Marta M Lenartowski Robert R

Planta 20170111 5

<h4>Main conclusion</h4>Calreticulin is involved in stabilization of the tip-focused Ca <sup>2+</sup> 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<sup>2+</sup>) gradient seems to be critical for pollen germination and pollen tube growth. We hypothesize that calreticulin (CRT), a Ca<sup>2+</sup>-binding/buffering c ...[more]

PMID: 28078426

Similar Datasets

Project description:BackgroundPollen 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 (Ca2+). Work from our laboratory and others provide evidence that calreticulin (CRT), a prominent Ca2+-binding/buffering protein in the endoplasmic reticulum (ER) of eukaryotic cells, may be involved in pollen formation and function. Here, we show for the first time the expression pattern of the PhCRT1 gene and CRT accumulation in relation to exchangeable Ca2+ in Petunia hybrida developing anther, and discuss probable roles for this protein in the male gametophyte development.ResultsUsing northern hybridization, western blot analysis, fluorescent in situ hybridization (FISH), immunocytochemistry, and potassium antimonate precipitation, we report that PhCRT1 is highly expressed in the anther and localization pattern of the CRT protein correlates with loosely bound (exchangeable) Ca2+ during the successive stages of microsporo/gametogenesis. We confirmed a permanent presence of both CRT and exchangeable Ca2+ in the germ line and tapetal cells, where these factors preferentially localized to the ER which is known to be the most effective intracellular Ca2+ store in eukaryotic cells. In addition, our immunoblots revealed a gradual increase in CRT level from the microsporocyte stage through the meiosis and the highest CRT level at the microspore stage, when both microspores and tapetal cells show extremely high secretory activity correlated with the biogenesis of the sporoderm.ConclusionOur present data provide support for a key role of CRT in developing anther of angiosperms - regulation of Ca2+ homeostasis during pollen grains formation. This Ca2+-buffering chaperone seems to be essential for pollen development and maturation since a high rate of protein synthesis and protein folding within the ER as well as intracellular Ca2+ homeostasis are strictly required during the multi-step process of pollen development.

Dataset Information

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

Publications

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

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets