A plant plasma membrane Ca ²⁺ pump is required for normal pollen tube growth and fertilization

Abstract

Ca 2؉ signals are thought to play important roles in plant growth and development, including key aspects of pollen tube growth and fertilization. The dynamics of a Ca 2؉ signal are largely controlled by influx (through channels) and efflux (through pumps and antiporters). The Arabidopsis genome encodes 14 Ca 2؉ pumps, 10 of which belong to a family of autoinhibited Ca 2؉ ATPases (ACA) that are predicted to be activated by Ca 2؉ ͞calmodulin. Here, we show that isoform ACA9 is expressed primarily in pollen and localized to the plasma membrane. Three independent T-DNA [portion of the Ti (tumor-inducing) plasmid that is transferred to plant cells] gene disruptions of ACA9 were found to result in partial male sterility. Complementation was observed by using a ACA9-yellow fluorescence protein (YFP) fusion that displayed plasma membrane localization. Mutant aca9 pollen displayed a reduced growth potential and a high frequency of aborted fertilization, resulting in a >80% reduction in seed set. These findings identify a plasma membrane Ca 2؉ transporter as a key regulator of pollen development and fertilization in flowering plants.

A P IIB -type Ca 2+ -ATPase is essential for stress adaptation in Physcomitrella patens

“…Ca 2+ -ATPases are thought to be the major components regulating [Ca 2+ ] cyt homeostasis. Physcomitrella PCA1 contains all characteristic motifs of plant P IIB -type Ca 2+ -ATPases, and its Ca 2+ -transport activity was substantiated by a yeast complementation where PCA1 displayed an identical mode of action already described for other plant P IIB -type Ca 2+ -ATPases (14,16,17).…”

“…To date, there are only 2 reported Arabidopsis P IIB -type Ca 2+ -ATPase gene KO lines, where the disruption of ACA9 caused partial male sterility, and disruption of ACA10 led to defects in vegetative growth and inflorescence architecture (17,19). Nevertheless, the expression pattern of other Ca 2+ -ATPase genes in Arabidopsis suggested a function of Ca 2+ -ATPases in abiotic stressrelated pathways (15).…”

“…Exploring the intracellular localization of Ca 2+ -ATPases may provide insights into the subcellular compartments that are involved in the maintenance of low [Ca 2+ ] cyt . Previous studies indicated a diverse localization of plant P IIB -type Ca 2+ -ATPases in the plasma membrane (17,36), the endoplasmic reticulum (ER) (37), small vacuoles (16), and the central vacuole (38). To analyze the localization of PCA1, we fused the cDNA of the GFP to the 3′ end of the PCA1 coding region under the control of the cauliflower mosaic virus 35S promoter and transfected the construct into Physcomitrella protoplasts that were analyzed by confocal laser scanning microscopy 48 h after the transformation.…”

“…Even though changes in [Ca 2+ ] cyt are associated with abiotic stress signaling there is as yet only indirect evidence for a role of plant Ca 2+ -ATPAses in stress signaling based on the ABA-responsive expression of the Arabidopsis genes ACA8 and ACA9 (15) and the acquirement of enhanced osmotolerance of a yeast strain overexpressing the Arabidopsis ACA4 gene (16). However, transgenic approaches have shown that plant Ca 2+ -ATPAses are involved in other fundamental processes such as pollen tube growth, vegetative development, inflorescence architecture, and gibberellin signaling (17)(18)(19). These studies suggest similar fundamental functions of P-type Ca 2+ -ATPases in plants and animals as the generation of KO mice revealed perturbations upon the targeted ablation of specific Ca 2+ -ATPases including lethality, tumorigenesis, skin and muscle diseases, deafness, balance disorders, and male infertility (20).…”

Species Preferentiality of the Pollen Tube Attractant Derived from the Synergid Cell ofTorenia fournieri

“…Although calcium has been detected in the synergid cell and the neighboring extracellular matrix, as described above (Jensen, 1965;Chaubal and Reger, 1990, 1992a, 1992bHuang and Russell, 1992;Tirlapur et al, 1993;Tian and Russell, 1997;Kristó f et al, 1999), Ca 21 may play a primary role in pollen tube discharge, gamete fusion, or both, but not in species-related pollen tube attraction. In an Arabidopsis mutant in which a plasma membrane Ca 21 pump of the pollen tube, ACA9, is disrupted, the pollen tube arrives at the embryo sac but cannot discharge its contents to the receptive synergid cell and shows overgrowth in the embryo sac (Schiøtt et al, 2004). ACA9 appears to be involved in intercell communication between the synergid cell and the pollen tube that triggers pollen tube discharge, along with the FERONIA and SIRENE genes that are expressed in the synergid cell (Huck et al, 2003;Rotman et al, 2003).…”