The plasma membrane-localised Ca(2+)-ATPase ACA8 plays a role in sucrose signalling involved in early seedling development in Arabidopsis.

KEY MESSAGE: Arabidopsis Ca (2+) -ATPase ACA8 plays a role in sucrose signalling during early seedling development by integrating developmental signals with carbon source availability. Calcium (Ca(2+)) is an essential signal transduction element in eukaryotic organisms. Changes in the levels of intracellular Ca(2+) affect multiple developmental processes in plants, including cell division, polar growth, and organogenesis. Here, we report that the plasma-membrane-localised Arabidopsis Ca(2+)-ATPase ACA8 plays a role in sucrose signalling during early seedling development. Disruption of the ACA8 gene elevated the expression of genes that encode transporters for Ca(2+) efflux. The seedlings that carried a T-DNA insertion mutation in ACA8 experienced water stress during early development. This response was unrelated to inadequate osmoregulatory responses and was most likely caused by disruption of cell membrane integrity and severe ion leakage. In addition, aca8-1 seedlings displayed a significant decline in photosynthetic performance and arrested root growth after removal of sucrose from the growth medium. The two phenomena resulted from impaired photosynthesis, reduced cell proliferation in the root meristem and the sucrose control of cell-cycle events. All of the stress-response phenotypes were rescued when expression of ACA8 was restored in aca8-1 mutant. Taken together, our results indicate that ACA8-mediated Ca(2+) signalling contributes to modulate early seedling development and coordinates root development with nutrient availability.