Arabidopsis Ca2+-ATPases 1, 2, and 7 in the endoplasmic reticulum contribute to growth and pollen fitness

Abstract

Generating cellular Ca2+ signals requires coordinated transport activities from both Ca2+ influx and efflux pathways. In Arabidopsis (Arabidopsis thaliana), multiple efflux pathways exist, some of which involve Ca2+-pumps belonging to the Autoinhibited Ca2+-ATPase (ACA) family. Here we show that ACA1, 2, and 7 localize to the endoplasmic reticulum (ER) and are important for plant growth and pollen fertility. While phenotypes for plants harboring single gene knockouts (KOs) were weak or undetected, a triple KO of aca1/2/7 displayed a 2.6-fold decrease in pollen transmission efficiency, whereas inheritance through female gametes was normal. The triple KO also resulted in smaller rosettes showing a high frequency of lesions. Both vegetative and reproductive phenotypes were rescued by transgenes encoding either ACA1, 2, or 7, suggesting that all three isoforms are biochemically redundant. Lesions were suppressed by expression of a transgene encoding NahG, an enzyme that degrades salicylic acid (SA). Triple KO mutants showed elevated mRNA expression for two SA-inducible marker genes, PR1 (Pathogenesis-related 1) and PR2. The aca1/2/7 lesion phenotype was similar but less severe than SA-dependent lesions associated with a double KO of vacuolar pumps aca4 and 11. Imaging of Ca2+ dynamics triggered by blue light or the pathogen elicitor flg22 revealed that aca1/2/7 mutants display Ca2+ transients with increased magnitudes and durations. Together, these results indicate that ER-localized ACAs play important roles in regulating Ca2+ signals, and that the loss of these pumps results in male fertility and vegetative growth deficiencies.

Transport, functions, and interaction of calcium and manganese in plant organellar compartments

“…Active import of Ca 2+ into the plant ER is likely mediated by P 2A - and P 2B -type ATPases, of which ECA1 ( Liang et al, 1997 ) and ACA1, 2, and 7 ( Harper et al, 1998 ; Rahmati Ishka et al, 2021 ) have been localized to this compartment.…”

“…ACA1, 2, and 7 are functionally redundant ( Rahmati Ishka et al, 2021 ). Loss of the three genes caused a defect in pollen transmission and aberrances in immunity, such as salicylic acid-dependent lesions in leaves, a phenotype also found in plants devoid of vacuolar ACAs (see below).…”

A Ratiometric Calcium Reporter CGf Reveals Calcium Dynamics Both in the Single Cell and Whole Plant Levels Under Heat Stress

“…The CGf reporter also showed that heat-triggered signals were approximately 1.5-fold greater in magnitude than the blue light signals in the same leaves (Figure 4). Blue light signals were previously documented using aequorin (Harada et al, 2003), YCnano65, and a GCaMP6 (Ishka et al, 2021). Evidence indicates that blue light activates phototropin receptors that trigger a Ca 2+ induced Ca 2+ release from internal Ca 2+ stores (Harada and Shimazaki, 2007).…”

A Molecular Pinball Machine of the Plasma Membrane Regulates Plant Growth—A New Paradigm

“…While the pinball machine and Hechtian oscillator emphasise influx, Ca 2+ homeostasis demands a finely balanced efflux evidenced by the fifteen Ca 2+ -ATPase pumps located in both the ER and plasma membrane of Arabidopsis [61].…”