Researchers have discovered a new stop in the recycling of plant organelles

The "hub-and-spoke" system enables plant cells to efficiently coordinate cell transport, especially cell recovery, the so-called autophagy process
.
Specialized vesicles, i.
e.
autophasomes, engulf harmful molecules and bring them to the vacuole for degradation
.
In this process, autophagosomes mature
using molecular mechanisms that are poorly understood in plants.
Now, researchers from the Gregor Mendel Institute of Molecular Plant Biology at the Austrian Academy of Sciences (GMI) describe the mechanism
by which autophagy uses the spoke pattern in plant cells.

Initially, autophagy was thought to be a survival process
for cells under starvation or stress.
However, autophagy is increasingly understood as a quality control mechanism that ensures the proper functioning
of cells by recycling excess or harmful components from them.
With the help of autophagy, cells replenish their molecular resources and produce some of the energy
needed to cope with changes in the environment.

Autophagy is carried out
by autophasomes (double membrane vesicles that engulf degraded substances).
Autophagosomes are organelles that are born, mature, and die, and we know quite a bit about how autophagosomes are born, but much less about their maturation pathways and delivery to their final destination, especially for plant cells
.
In plant cells, the "final destination" is vacuole, a large organelle that makes up about 80 percent of the cell's volume and is filled with digestive enzymes
.

Many sacic organelles, such as autophagosomes, function in cells; They move through the cells in a carefully arranged way to mature and fulfill their function
.
In their latest paper, Dagdas and his team show that plant autophagosomes do not follow a direct, linear path as they enter the vacuole
.
"We don't yet know if this applies to all plant autophagosomes, but we show that at least some of them stay in different locations before reaching the vacuole," Dagdas said
.

Using complementary approaches from biochemistry, cell imaging, and structural biology, the researchers showed that plant autophagosomes first fuse with other endoplastid organelles called "polyvesicles" (MVBs) to form so-called "amphoterics.
"
The amphoterics then fuse
with the vacuole.

At the heart of their research was the discovery of the autophagy adapter CFS1, a molecule that recognizes membrane-labeled autophasomes and MVBs and therefore mediates their fusion
.
The researchers demonstrated the function of amphoterics as cell sorting centers, maturation and transport of autophagosomes to vacuoles
.

"The trafficking routes are quite complex, but they all need to be coordinated, and for cells, the energy to produce vesicles is very
high.
Therefore, we believe that by using amphoterics as sorting centers for autophagosomes, the cell optimizes its energy efficiency
.
The scientists compared
this sortation center model to "spoke-and-spoke" systems in the aviation industry and other supply chain logistics.
"By having all the materials transported through a centralized hub, the unit reduces its logistics costs because fewer
routes are required.
In addition, this system makes cells more economical because complex operations can be performed in collectives rather than individually organized in each autophagosome.
"

The researchers confirmed the function of the autophagy adapter CFS1 in two highly evolved plant model organisms: Arabidopsis thaliana and Marchantia polymorpha, so this autophagosome maturation mechanism is conserved in plants
.
Since autophagy plays a central role in regulating cellular stress, this study may find future applications in plant bubble transport engineering to help improve plant resilience
.