The ABA-regulated Arabidopsis TSPO is an ER/Golgi localized heme binding membrane protein and a potential scavenger of porphyrins via an autophagy-dependent degradation mechanism

Plants are sessile organisms and therefore are affected by different environmental challenges, including salinity, drought, high light, high temperature or freezing (generically referred to as abiotic stresses). These conditions can be perceived, in part, as a transient or permanent water deficit and result in the accumulation of the stress phytohormone abscisic acid (ABA), which regulates the expression of ABA-responsive genes. Some of these ABA-induced proteins are only transiently expressed, and therefore the plant cell needs an efficient regulatory mechanism for transcriptionally and/or post-translationally regulating their expression/degradation. Although many transcriptional regulatory mechanisms have been characterized, the question of how, when and where transiently ABA-induced proteins are targeted for degradation has not been addressed. Here we present a case study for the Arabidopsis thaliana Translocator-related (AtTSPO) membrane protein, transiently induced by abiotic stresses. Our data show a complex interaction between heme binding and subsequent selective autophagy, resulting in downregulation of AtTSPO and probably the scavenging of excess heme through this mechanism. These findings represent the first report of heme-dependent protein degradation in higher plants. The expression of AtTSPO also has a physiological role during stress, since the protein can alleviate induced porphyria in the plant cell. Furthermore, plants that constitutively express AtTSPO are less sensitive to iron starvation, but more sensitive to iron toxicity.(BIOL 3) -- UCL, 201