An investigation into the role of Small Ubiquitin-like MOdifier (SUMO) in plant response to phosphate deficiency

Rice (Oryza sativa) is a staple food crop for more than half of the world’s population and provides 20% of dietary energy all over the world. Although it is the main source of calories, nearly 60% of rice is grown in soils which are low in phosphorus especially in Asia and Africa. Inorganic Phosphate (Pi) is a non-renewable and indispensable macroelement for plant growth. Pi levels in soil are modulated by interaction with other elements such as aluminium and iron. This interaction between other elements regulates the availability of Pi to plants even after the application of fertilizers. Given the limitations of bioavailable Pi in soils, it is important to develop crops tolerant to low phosphate. This would be helpful to resource-poor farmers. Due to their immobile nature plants have developed complex molecular signalling pathways that allows them to discern changes in the environment and adapt their growth and development. Post Translation Modifications (PTMs) play an important role in plants in providing a conduit to detect the changing environment and influence molecular signalling pathways to adapt growth and development. In recent years the PTM SUMOylation has been shown to be critical for plant growth and development. It is known that plants experience hyperSUMOylation of target proteins during stresses such as heat, salinity, drought and phosphate starvation. We provide new evidence for the role of SUMO in plant responses to Pi starvation. Here we demonstrate that PSTOL1 is SUMOylated in planta, and this affects its autophosphorylation activity. Moreover, we have investigated the targets of PSTOL1 using yeast two hybrid and coimmunoprecipitation techniques. Further, we also provide new evidence for the role of SUMO in plant responses to Pi starvation in rice and Arabidopsis. Our data demonstrated that overexpression of non – SUMOylatable version of OsPSTOL1 negatively affects the root parameters of rice grown under low Pi. Interestingly, our data also showed that overexpression of PSTOL1 in a heterologous system, Arabidopsis positively impacts overall plant growth under high and low Pi by modulating root system architecture. Therefore, unraveling the role of SUMOylation to improve plants’ ability to survive in phosphorus-deficient soil will open-up new ways to enhance the productivity of rice varieties.