Protein interactions improve fungal symbiosis in tomato plants

Researchers have discovered how two proteins interact to enhance the symbiosis between tomato plants and arbuscular mycorrhizal fungi (AMF), which favors phosphorus (P) uptake by the plants. The study reveals that the SlDELLA protein binds to SlPIF4, reducing its stability and transcriptional activity, thus promoting the development of the symbiosis and phosphorus utilization.

Arbuscular mycorrhizal symbiosis (AMS) is essential for plants to obtain phosphorus in agricultural soils, where this nutrient, despite being abundant, has low mobility and availability. Fungi supply phosphorus to the plant in exchange for carbohydrates. In tomato plants, this interaction is favored by strigolactones (SLs), hormones that stimulate fungal growth in the soil.

The study showed that SlPIF4 acts as a negative regulator of AMS and symbiosis-induced phosphorus uptake. Plants engineered to overexpress SlPIF4 showed reduced fungal colonization, while mutants deficient in this protein showed increased colonization and elevated levels of symbiosis-specific phosphate transporters (PT4 and PT5).

SlDELLA, in turn, physically interacts with SlPIF4 and reduces its stability, promoting the accumulation of SLs and the expression of the PT4 and PT5 genes. In SlDELLA-deficient mutants, symbiosis was impaired, even when SlPIF4 was absent, indicating that SlDELLA acts upstream in regulation.

The authors state that SlPIF4 binds directly to the promoter regions of genes involved in SL biosynthesis and phosphate transporters, inhibiting their transcription. The presence of SlDELLA prevents this binding, favoring the expression of these genes and, consequently, symbiosis and phosphorus uptake.

The research proposes that genetically manipulating the levels of these proteins could be a strategy for increasing the efficiency of phosphorus use, a limited resource in agriculture. According to the authors, the SlDELLA-SlPIF4-SLs/PTs signaling pathway represents a promising target for developing tomato cultivars that better utilize soil phosphorus.

More information at doi.org/10.1093/hr/uhae195

Understand the terms

• SlDELLA: scientific abbreviation referring to the DELLA protein found in the tomato species. Sl: is the abbreviation for the genus and species of tomato: Solano lycopersicumIn biology, it is common to use the first two letters of the genus and the first two letters of the species to identify the origin of the protein or gene. DELLA: refers to a specific family of regulatory proteins in plants. DELLA proteins are known to be repressors of the gibberellin (GA) signaling pathway, which are plant hormones that promote growth.

• SlPIF4: abbreviation for Solanum lycopersicum Phytochrome-Interacting Factor 4. Sl: refers to the tomato. PIF4: stands for Phytochrome-Interacting Factor 4. PIFs (phytochrome-interacting factors) are a family of proteins found in plants. They are transcription factors, meaning they bind to DNA to control the expression of other genes.