A phosphate starvation response-regulated receptor-like kinase, OsADK1, is required for mycorrhizal symbiosis and phosphate starvation responses

Most land plants associate with arbuscular mycorrhizal (AM) fungi to secure mineral nutrient acquisition, especially that of phosphorus. A phosphate starvation response (PHR)-centered network regulates AM symbiosis. Here, we identified 520 direct target genes for the rice transcription factor OsPHR1/2/3 during AM symbiosis using transcriptome deep sequencing and DNA affinity purification sequencing. These genes were involved in strigolactone biosynthesis, transcriptional reprogramming, and bidirectional nutrient exchange. Moreover, we identified the receptor-like kinase, Arbuscule Development Kinase 1 (OsADK1), as a new target of OsPHR1/2/3. Electrophoretic mobility shift assays and transactivation assays showed that OsPHR2 can bind directly to the P1BS elements within the OsADK1 promoter to activate its transcription. OsADK1 appeared to be required for mycorrhizal colonization and arbuscule development. In addition, hydroponic experiments suggested that OsADK1 may be involved in plant Pi starvation responses. Our findings validate a role for OsPHR1/2/3 as master regulators of mycorrhizal-related genes involved in various stages of symbiosis, and uncover a new RLK involved in AM symbiosis and plant Pi starvation responses.

Automated summary

In this study, we identified 520 direct target genes for the rice transcription factor OsPHR1/2/3 during arbuscular mycorrhizal (AM) symbiosis. These genes are involved in strigolactone biosynthesis, transcriptional reprogramming, and bidirectional nutrient exchange. We also discovered that OsPHR2 can directly bind to the promoter region of Arbuscule Development Kinase 1 (OsADK1) to activate its transcription, which is required for mycorrhizal colonization and arbuscule development. Furthermore, we found that OsADK1 may play a role in plant phosphate starvation responses. Our study confirms the crucial role of OsPHR1/2/3 as master regulators of mycorrhizal-related genes and identifies a new receptor-like kinase (RLK) involved in AM symbiosis and plant phosphate starvation responses.