Abstract
BackgroundPlant annexins are calcium- and lipid-binding proteins that have multiple functions, and a significant amount of research on plant annexins has been reported in recent years. However, the functions of annexins in diverse biological processes in rice are largely unclear.ResultsHerein, we report that OsANN4, a calcium-binding rice annexin protein, was induced by abscisic acid (ABA). Under ABA treatment, the plants in which OsANN4 was knocked down by RNA interference showed some visible phenotypic changes compared to the wild type, such as a lower rooting rate and shorter shoot and root lengths. Moreover, the superoxide dismutase (SOD) and catalase (CAT) activities of the RNAi lines were significantly lower and further resulted in higher accumulation of O2.- and H2O2 than those of the wild-type. A Non-invasive Micro-test Technology (NMT) assay showed that ABA-induced net Ca2+ influx was inhibited in OsANN4 knockdown plants. Interestingly, the phenotypic differences caused by ABA were eliminated in the presence of LaCl3 (Ca2+ channel inhibitor). Apart from this, we demonstrated that OsCDPK24 interacted with and phosphorylated OsANN4. When the phosphorylated serine residue of OsANN4 was substituted by alanine, the interaction between OsANN4 and OsCDPK24 was still observed, however, both the conformation of OsANN4 and its binding activity with Ca2+ might be changed.ConclusionsOsANN4 plays a crucial role in the ABA response, partially by modulating ROS production, mediating Ca2+ influx or interacting with OsCDPK24.
Highlights
Plant annexins are calcium- and lipid-binding proteins that have multiple functions, and a significant amount of research on plant annexins has been reported in recent years
OsANN4, is responsive to Abscisic acid (ABA) Based on bioinformatics, there are ten putative annexin genes in the rice genome, and we previously reported that OsANN1, OsANN3 and OsANN10 are involved in the response to heat, drought and osmotic stress [36,37,38]
A sequence search based on the NCBI database revealed that the protein contains three annexin domain architectures, so-called annexin repeats, Fig. 1 OsANN4 responds to exogenous abscisic acid in rice. a Schematic diagram of the gene structure and protein domain of OsANN4
Summary
Plant annexins are calcium- and lipid-binding proteins that have multiple functions, and a significant amount of research on plant annexins has been reported in recent years. Abscisic acid (ABA), a well-known long-distance signaling molecule utilized for communication between plant roots and shoots under water-deficient conditions, is considered a hormone that plays a critical role in abiotic stress tolerance in plants [1, 2]. The massive accumulation of ROS leads to redox imbalance, causing protein, DNA and lipid damage and even the death of plants [17, 18]. To ensure the proper function and survival of plant cells, it is very important to rapidly eliminate the massive ROS. The defense system of enzymatic scavengers, including catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR), plays an essential role in the elimination of ROS [19, 20]
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