Genome-wide Analysis Of The Phosphorus Starvation Response Mechanism In Rice And The Role Of Regulator OsPHR2 On Phosphorus Deficient Adaptation

It is of great practical significance on plant genetic improvement to clarify molecular mechanism of plant strategy to adapt to P starvation for efficiency Phosphate(Pi) utilization.In this study,global changes in the expression of Pi-responsive genes in rice and CTK-responsive were investigated through microarray analysis.OsPHR2 is an important factor of Pi-starvation signaling.The transgenic plants with overexpression and repression of OsPHR2 were also used to investigate its effect on Pi signalling in rice.The results are summarized as follows:1)Pi-starvation change Pi concentration in riceAfter 10 day treatment,the difference of fresh weight of plant under different Pi conditions was slight,while the Pi concentration is changed a lot.Under Pi sufficient condition,the Pi concentration maintained at a stable level(approximately 0.9mg/gFW in shoot and 0.4mg/gFW in root).While under Pi starvation,Pi concentration was decreased by about 92%and 97%in shoots and roots,respectively.2)Metabolism changed under Pi starvation conditionMany genes in glycolysis and alternative energy metabolism were found to be invoked to provide carbon substrates and replace Pi- and adenylaterequiring enzymes in nutrient-sufficient status.Phospholipase D,SQD1 and SQD2 for sulpholipid biosynthesis,were also found to be induced by Pi starvation in our study.It suggests that 10-day Pi-starvation treatment was enough to trigger physiological and biochemical adaptations upon the 14- day-old rice seedlings.3)Cytokinin influenced the Pi concentration under Pi starvation conditionUnder Pi sufficient condition at day 10,the Pi concentration was not significantly changed in shoots by the exogenous CTK,while increased by 80%in roots.However, under Pi-starvation condition,Pi concentration was increased by three- and six fold in shoots and roots,respectively,with exogenous CTK(6BA).The combined effect of CTK and Pi-starvation signal features a global reduction of Pi-starvation signalling triggered by the exogenous CTK with a remarkable increase of the cellular Pi concentration.This suggests that the increase of cellular Pi level caused by exogenous CTK treatment is likely to be one of the mechanisms for repression of systemic Pi-starvation signalling by CTK4)OsPHR2 overexpression upregulated the expression of a subset of PSI genesThe overexpression of OsPHR2 upregulated the expression of a subset of Pi-starvation inducible(PSI)genes under both Pi sufficient and Pi starvation conditions, while the repression of OsPHR2 reduced the expressions of the Pi-starvation-inducible genes.These results indicate that OsPHR2 plays an important role in phosphorus starvation signalling in rice,and the function of OsPHR2 on Pi signaling is differ with CTK since they influenced Pi signaling under different Pi conditions.5)OsPHR2 and CTK have opposite effects on Pi signalingCTK and OsPHR2 are both involved in Pi signaling and PHR2 mainly influences the Pi signaling under Pi deficiency condition,while CTK have a great effect on Pi signaling under Pi sufficiency.The expression of CRE1 is not change in OsPHR2 overexpression plants and the OsPHR2 expression is not changed after CTK treatment. So it is reasonable to consider that the effects of OsPHR2 and CTK on Pi signaling are opposite and they effect Pi signaling under different Pi conditions.