Unconventional protein secretion (UPS) in plants includes various transport routes of protein (e.g. extracellular vesicles and Endoplasmic Reticulum (ER) - derived vesicles) alternative to the conventional secretory pathway. However, an exhaustive comprehension of these unconventional pathways and of their molecular mechanisms remain elusive. Recently, secretome analysis revealed that different types of secreted proteins, including leaderless secretory proteins (LSPs), were found in the extracellular space of plant cells. LSPs may represent over 50% of the total secretome identified in plants, supporting the existence of novel mechanisms of secretion that are independent from the conventional ER-Golgi secretory pathway. Moreover, several proteins were also identified that, although containing a signal peptide, reach various compartments, such as the vacuole or endosymbiont organelles, by UPS routes. Here we report three cases study of human or plant proteins that are secreted according to UPS in plant cells: i) human lysosomal ?-mannosidase (MAN2B1), ii) human indoleamine 2,3-dioxygenase 1 (IDO1), iii) plant CLAVATA3 (CLV3). MAN2B1 has a signal peptide and in animal cells is transported to lysosomes trough the Golgi complex with a conventional pathway. Conversely, when expressed in plants, MAN2B1 is targeted to the vacuole by a UPS pathway thanks to a putative vacuolar targeting signal located in the amino-terminal domain. The immunoregulatory human IDO1 does not contain a signal peptide and it is secreted in the extracellular space according to a UPS pathway, both in mammals and in plant cells. Finally, we described the transport and maturation process of the plant stem cell regulatory protein CLV3, from which a biological active 12-14 amino acid peptide is released and extracellularly secreted. Although containing a signal peptide, the pathway of CLV3 processing deviates from the conventional secretory pathway and is subjected to proteasomal degradation, leading to secretion of the active peptide through a putative UPS mechanism.
Unconventional protein secretion in plant cells: three cases study
Francesca De Marchis;Michele Bellucci;
2019
Abstract
Unconventional protein secretion (UPS) in plants includes various transport routes of protein (e.g. extracellular vesicles and Endoplasmic Reticulum (ER) - derived vesicles) alternative to the conventional secretory pathway. However, an exhaustive comprehension of these unconventional pathways and of their molecular mechanisms remain elusive. Recently, secretome analysis revealed that different types of secreted proteins, including leaderless secretory proteins (LSPs), were found in the extracellular space of plant cells. LSPs may represent over 50% of the total secretome identified in plants, supporting the existence of novel mechanisms of secretion that are independent from the conventional ER-Golgi secretory pathway. Moreover, several proteins were also identified that, although containing a signal peptide, reach various compartments, such as the vacuole or endosymbiont organelles, by UPS routes. Here we report three cases study of human or plant proteins that are secreted according to UPS in plant cells: i) human lysosomal ?-mannosidase (MAN2B1), ii) human indoleamine 2,3-dioxygenase 1 (IDO1), iii) plant CLAVATA3 (CLV3). MAN2B1 has a signal peptide and in animal cells is transported to lysosomes trough the Golgi complex with a conventional pathway. Conversely, when expressed in plants, MAN2B1 is targeted to the vacuole by a UPS pathway thanks to a putative vacuolar targeting signal located in the amino-terminal domain. The immunoregulatory human IDO1 does not contain a signal peptide and it is secreted in the extracellular space according to a UPS pathway, both in mammals and in plant cells. Finally, we described the transport and maturation process of the plant stem cell regulatory protein CLV3, from which a biological active 12-14 amino acid peptide is released and extracellularly secreted. Although containing a signal peptide, the pathway of CLV3 processing deviates from the conventional secretory pathway and is subjected to proteasomal degradation, leading to secretion of the active peptide through a putative UPS mechanism.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
