Abstract
Annexins are a superfamily of soluble calcium-dependent phospholipid-binding proteins that have considerable regulatory effects in plants, especially in response to adversity and stress. The Arabidopsis thaliana AtAnn1 gene has been reported to play a significant role in various abiotic stress responses. In our study, the cDNA of an annexin gene highly similar to AtAnn1 was isolated from the cassava genome and named MeAnn2. It contains domains specific to annexins, including four annexin repeat sequences (I–IV), a Ca2+-binding sequence, Ca2+-independent membrane-binding-related tryptophan residues, and a salt bridge-related domain. MeAnn2 is localized in the cell membrane and cytoplasm, and it was found to be preferentially expressed in the storage roots of cassava. The overexpression of MeAnn2 reduced the sensitivity of transgenic Arabidopsis to various Ca2+, NaCl, and indole-3-acetic acid (IAA) concentrations. The expression of the stress resistance-related gene AtRD29B and auxin signaling pathway-related genes AtIAA4 and AtLBD18 in transgenic Arabidopsis was significantly increased under salt stress, while the Malondialdehyde (MDA) content was significantly lower than that of the control. These results indicate that the MeAnn2 gene may increase the salt tolerance of transgenic Arabidopsis via the IAA signaling pathway.
Highlights
Annexins, similar to calmodulins, are multifunctional phospholipid-binding proteins that bind calcium ions and phospholipids in the membrane in response to external stimuli
The convex side of annexin is oriented toward the biofilm and the concave side is oriented toward the cytoplasm when the annexin as mediated by Ca2+, and the N-terminal domain can interact with other proteins or molecules in the cytoplasm as part of the annexin function [1,3,4]
Most of the known plant annexins are mainly located in the cytoplasm, while some are distributed in the plasma membrane, organelle membranes, nuclear membrane, and nucleoli [5]
Summary
Similar to calmodulins, are multifunctional phospholipid-binding proteins that bind calcium ions and phospholipids in the membrane in response to external stimuli. The membrane binding sites of each repeat are located in the helix A-B and helix D-E loops which are belong to the convex side of the disk structure [3]. Annexin can be transferred within plants under different stress environments [8], and the expression of annexin in tissues varies greatly with the growth and development of plants [9,10,11,12,13]. This demonstrates that annexins, as functional proteins, are involved in the regulation of plant metabolism, growth, and development. The observation and analysis of transgenic Arabidopsis roots successfully transfected using annexin tagged with green fluorescent protein (GFP) revealed that annexin could promote Ca2+ influx in Arabidopsis protoplasts, thereby increasing intracellular Ca2+ concentrations [14,15,16]
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