Maira Diaz, Maria Jose Sanchez-Barrena, Juana Maria Gonzalez-Rubio, Lesia Rodriguez, Daniel Fernandez, Regina Antoni, Cristina Yunta, Borja Belda-Palazon, Miguel Gonzalez-Guzman, Marta Peirats-Llobet, Margarita Menendez, Jasminka Boskovic, Jose A. Marquez, Pedro L. Rodriguez, and Armando Albert

Significance

Drought and salinity are the major threats to crop productivity at a worldwide scale. A fundamental portion of the plant response to these environmental stresses occurs at the cell membrane, where the molecular machinery to preserve cell turgor and the appropriate balance of intracellular ions is found. The C2-domain ABA-related (CAR) family of proteins contributes to these processes by delivering the regulatory proteins controlling this machinery from other cell compartments to the cell membrane. Our analysis provides an explanation on how CAR proteins specifically reach a particular membrane place to develop their function and trigger the plant defense mechanism against stress.

Abstract

Regulation of ion transport in plants is essential for cell function. Abiotic stress unbalances cell ion homeostasis, and plants tend to readjust it, regulating membrane transporters and channels. The plant hormone abscisic acid (ABA) and the second messenger Ca²⁺ are central in such processes, as they are involved in the regulation of protein kinases and phosphatases that control ion transport activity in response to environmental stimuli. The identification and characterization of the molecular mechanisms underlying the effect of ABA and Ca²⁺ signaling pathways on membrane function are central and could provide opportunities for crop improvement. The C2-domain ABA-related (CAR) family of small proteins is involved in the Ca²⁺-dependent recruitment of the pyrabactin resistance 1/PYR1-like (PYR/PYL) ABA receptors to the membrane. However, to fully understand CAR function, it is necessary to define a molecular mechanism that integrates Ca²⁺ sensing, membrane interaction, and the recognition of the PYR/PYL interacting partners. We present structural and biochemical data showing that CARs are peripheral membrane proteins that functionally cluster on the membrane and generate strong positive membrane curvature in a Ca²⁺-dependent manner. These features represent a mechanism for the generation, stabilization, and/or specific recognition of membrane discontinuities. Such structures may act as signaling platforms involved in the recruitment of PYR/PYL receptors and other signaling components involved in cell responses to stress.

See: http://www.pnas.org/content/113/3/E396.abstract.html?etoc

PNAS January 19, 2016; vol. 113, no.3: E396–E405

Fig. S2. The ribbon representation of the crystal structures of CAR4 (Left) and CAR1 (Right).