Investigating the role of stromules in scent (monoterpene) emission and hormone secretion by plants

Stromules and scent emission:

Stromules are highly dynamic small membrane tubes emanating from chloroplasts and plastids. Stromules can get very long , form branches and cause a large increase in the surface area of plastids, enabling more efficient metabolite exchange with other cellular compartments. Stromules can connect plastids with each other and can connect plastids with other membrane compartments of the cell like ER, Golgi, plasma membrane, mitochondria and peroxisomes.

Monoterpenes are synthesised in the plastids and once emitted they are part of the plant scent bouquet. At present it is not clear how the monoterpenes are transported from the plastid to the plasma membrane for release into the headspace.

Stromules and hormone secretion:

Plastids produce the phytohormone strigolactones which are involved in suppression of branching in the plant and mobilization of Arbuscular mycorrhizal (AM) fungi around the root of the plant. It is known that under phosphate limitation in the soil, roots start to produce more strigolactones, which are secreted to the soil and help AM fungi in branching to obtain a larger surface area to aid the plant in phosphate uptake from the soil. It is also known that under P limitation the number of contact sites between plastids and ER increases. However, it is not known what the role of stromules are in establishing plastid-ER contact sites.

Studying stromules by manipulating stromule activity

The formation of stromules requires a certain fluidity of the plastid membrane. Since monoterpenes sequester into membranes and increase their fluidity, we want to investigate whether plant cells that overproduce monoterpenes have more stromule activity.

The mobility of stromules is mediated by myosin XI motor proteins that pull these structures over a fine-actin network surrounding the plastids. By inhibiting myosin XI activity with an RNAi construct,  we want to test the effect of myosin RNAi on stromule activity and monoterpene emission by plants.

We want to compare stromule activity of plastids in roots with and without phosphate stress to determine if stromules are involved in the increase in ER contact sites under phosphate stress. Since phosphate stress induces the production of the phytohormote strigolactone, we will investigate if this phytohormone by itself can cause changes in the number of ER contact sites by using plnats that cannot produce strigolactones.