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Title: Disruption of the vacuolar calcium-ATPases in arabidopsis results in the activation of a salicylic acid-dependent programmed cell death pathway

Author
item BOURSIAC, YANN - University Of Nevada
item LEE, SANG MIN - University Of Nevada
item ROMANOWSKY, SHAWN - University Of Nevada
item Blank, Robert - Bob
item SLADEK, CHRIS - University Of Nevada
item CHUNG, WOO SIK - Gyeongsang National University
item HARPER, JEFFREY - University Of Nevada

Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2010
Publication Date: 9/13/2010
Citation: Boursiac, Y., Lee, S., Romanowsky, S., Blank, R.R., Sladek, C., Chung, W., Harper, J. 2010. Disruption of the vacuolar calcium-ATPases in arabidopsis results in the activation of a salicylic acid-dependent programmed cell death pathway. Journal of Plant Physiology. 154:1158-1171.

Interpretive Summary: Calcium in plants regulate a variety of responses to the environment, including a programmed cell death (PCD) that protects them from pathogens. Calcium signals are determined by influx channels and efflux pumps or cotransporters. Only two calcium pumps have been located at the vacuolar membrane and loss of their function triggers a PCD-like response visible as lesions on the entire leaves. Lesions appearance was prevented by genetically reducing the accumulation of the plant hormone salicylic acid, or by a novel hydroponic culture media containing at least 15 to 20mM anions. Under those conditions, transpiration in the double mutant was increased, demonstrating a role of the vacuolar calcium pumps in controlling multiple aspects of cellular physiology, including a programmed cell death pathway and transpiration.

Technical Abstract: Calcium (Ca2+) signals regulate many aspects of plant development, including the Hypersensitive Response (HR) that triggers a programmed cell death response to protect a plant from a pathogen. A transient increase in cytosolic Ca2+ ([Ca2+]cyt ) results from Ca2+ entry from the apoplast or release from internal stores (e.g., the vacuole). A return to steady state [Ca2+]cyt levels is achieved through calcium/proton exchangers (CAX) or calcium pumps (ECA and ACA). In Arabidopsis, two calmodulin-activated Ca2+ Pumps (ACA4 and ACA11) have been found located in the tonoplast. Here we show that a double mutation of these two pumps results in a high frequency of HR-like lesions in plants growing under normal conditions. Lesions could be suppressed by disrupting the production or accumulation of salicylic acid (SA), as shown by combining aca4/11 mutations with a sid2 mutation or expression of a NhaG SA degradation enzyme. A novel conditional suppression was observed when nutrient supplies were supplemented with high (> 15 mM) levels of either phosphate, nitrate, or chloride. This conditional suppression was lost within three days of moving plants to more normal nutrient conditions. Lesion onset was found to originate primarily in mesophyll cells, as indicated by the appearance of micro-lesions detected by aniline blue staining. Under nutritional conditions that suppress lesions, aca4/11 also exhibited a higher transpiration rate, indicating that the vacuolar pumps help regulate calcium signaling pathways other than those that trigger programmed cell death. Altogether, those data demonstrate a role of the vacuolar calcium pumps in controlling multiple aspects of cellular physiology, including a programmed cell death pathway.