Suppressor of apoptosis. Modulator of endoplasmic reticulum stress-mediated programmed cell death. Involved in methyl jasmonate-induced leaf senescence through regulating cytoplasmic calcium level. Interacts (via C-terminus) with calmodulin, CYTB5-B and CYTB5-D. Interacts indirectly with FAH1 via CYTB5-D. Expressed in root tips, root vasculature, flower tissues, including stamens and sepals, and in the base of siliques. Not detected in mature leaves. Up-regulated by water stress, heat-shock, mycotoxin and pathogens. No visible phenotype under normal growth conditions. Accelerated methyl jasmonate-induced leaf senescence. Enhanced sensitivity to water stress, heat shock, toxin, tunicamycin and pathogens. Belongs to the BI1 family.