Figure 1 A proposed model of malate-regulated programmed cell death in plants (modified from Zhao et al., 2018; Heng et al., 2018)(A) In Arabidopsis thaliana, MOD1 encodes an enoyl-acyl carrier protein reductase, the deficiency of MOD1 causes an increased level of NADH in the chloroplasts, which drives oxaloacetate (OAA) to be converted to malate by plNAD-MDH. Malate is transported out of the chloroplast into the cytosol by DiT1, and then be transported into the mitochondrion by an unidentified transporter or transporters. In the mitochondrion, malate is converted to OAA by mMDH1, and simultaneously NADH is generated to provide electrons for mETC to induce ROS formation and initiate programmed cell death (PCD) process in the mod1 cells. (B) In Oryza sativa, OsALMT7 encodes a putative aluminum-activated plasma membrane localized malate transporter, which could transport malate into cells. Malate is involved in nuclear DNA stability and inhibits excessive accumulation of H2O2 and malondialdehyde, which protects cells from PCD. The paab1-1 mutant harbors a mutation in OsALMT7, and its panicle contained less malate than wild type, particularly at the apical portions. The apical spikelets in the paab1-1 mutant undergo PCD accompanied by nuclear DNA fragmentation and accumulation of higher levels of H2O2 and malondialdehyde.