Calcium (Ca2+) acts as a second messenger connecting the perception of pathogenic microbial signals to the establishment of appropriate immune responses in plants. Accumulating evidence suggests that plants distinguish different pathogenic microorganisms through plasma membrane-localized pattern recognition receptors. The particular recognition events are encoded into Ca2+ signatures, which are sensed by diverse intracellular Ca2+-binding proteins. The Ca2+ signatures are eventually decoded into distinct downstream responses through transcriptional reprogramming of defense-related genes. Recent observations further reveal that Ca2+ signaling-mediated AtSR1/CaMTA3 plays a crucial role in plant immune response. AtSR1 (Arabidopsis Signal Responsive 1 also known as CAMTA3, Calmodulin-binding Transcriptional Activator 3) is documented to suppress the expression of defense-related genes. Recent observation revealed that AtSR1 is identified as a guardee monitored by NLR guard proteins. It has been observed that plants encrypt the perception of different pathogenic stimuli, bacterial-derived flg22 and fungal-derived chitin, into specific intracellular Ca2+ signatures/transients and subsequently decrypt these Ca2+ transients/signatures into appropriate downstream responses through various Ca2+-binding proteins such as calmodulin to establish appropriate immune response in plants. In addition, recent data revealed AtSR1 was also involved in balancing plant growth through the brassinosteroid- and auxin-mediated pathways. EMSA (electrophoretic mobility shift assay) and other data indicated that AtSR1 was able to interact with multi targeted DNA-motif, in addition to the "CGCG" motif. In addition, AtSR1 was found to regulate transcriptional expression and function of NIM1, NON-INDUCIBLE IMMUNITY 1, which was reported to be a receptor for the plant defense hormone salicylic acid (SA) and a regulator in the SA-mediated systemic acquired resistance (SAR) pathway. In summary, these observations support a major role for Ca2+ signaling in launching and fine-tuning plant immune response, as well as AtSR1 acting as a hub for decoding Ca 2+ signals into appropriate immune response.