Phosphorus is an essential nutrient for plants, which must maintain constant internal levels of this compound. To achieve this, plant cells modulate the amount of phosphate transporter the assimilable form of phosphorus-- in the membrane.
This month, researchers at the Centro Nacional de Biotecnología (CNB-CSIC), in collaboration with other European centres, published an article in the journal Proceedings of the National Academy of Sciences USA and another in The Plant Cell. They describe the mechanism ALIX uses to regulate transporter traffic from the membrane to the degradation site inside the cell.
"When there is sufficient phosphate, the transporters are internalised and degraded in the vacuole. This reduces uptake of this nutrient by the cell", says Vicente Rubio, , a CNB researcher and lead author of one of the articles.
The ALIX protein has an essential role in classifying the content of vesicles that are directed to vacuoles, and in inducing the destruction of unnecessary elements. ALIX interacts with other proteins essential in this process such as the ESCRT complex or the AMSH deubiquitinases. "When ALIX is defective and non-functional, phosphate transporters are not degraded, and accumulate erroneously on the vacuole membrane. These defects alter the plant’s phosphate homeostasis", Rubio explains.
ALIX also regulates the intracellular trafficking and degradation of other membrane proteins. "Plants in which the ALIX protein is not fully functional grow less and bloom later. Moreover, inactivating mutations are lethal. This shows that ALIX is involved in processes essential to the life of the plant", says the scientist.
- Cardona-López X, Cuyas L, Marín E, Rajulu C, Irigoyen ML, Gil E, Puga MI, Bligny R, Nussaume L, Geldner N, Paz-Ares J, Rubio V. ESCRT-III-Associated Protein ALIX Mediates High Affinity Phosphate Transporter Trafficking to Maintain Phosphate Homeostasis in Arabidopsis. Plant Cell, 2015 Sep 4. pii: tpc.15.00393
- Kalinowska K, Nagel MK, Goodman K, Cuyas L, Anzenberger F, Alkofer A, Paz-Ares J, Braun P, Rubio V, Otegui MS, Isono E. Arabidopsis ALIX is required for the endosomal localization of the deubiquitinating enzyme AMSH3. Proc Natl Acad Sci USA, 2015 Aug 31. pii: 201510516.