Oxygen Deficient Stress And Flowering Time Regulationgene GIGANTEA Involve In Phosphate Homeostasis In Rice

Phosphorus (P) is an essential macronutrient required by plants to accomplish their life cycle. Although abundant P exists in the earth’s crust, little is present in the form of inorganic phosphate (Pi), which is available for plants. P fertilizer utilization brings many problems, including P resource consuming, increased cost, and environment pollution. Therefore, transgenic modification is critical for plants to satisfy the demand of modern agriculture. Investigation of Pi response mechanisms is of great importance for modifying crops with improved P utilizing efficiency. In our current study, we investigated the involvment of oxygen deficient stress and flowering time regulation gene GIGANTEA in phosphate homeostasis in rice.Overexpression of OsPHR2increases Pi uptake and causes Pi overaccumulation in rice grown in Pi sufficient culture, resulting in leaf tip necrosis. The toxicity in OsPHR2plants can be significantly alleviated by growing the plants in the waterlogged paddy field. A comparison of Pi uptake and growth status of OsPHR2overexpression plants grown in paddy fields or in a laboratory setting stagnant culture indicated that the oxygen limitation that is present in paddy fields and in stagnant rice culture solutions alleviates phosphate overaccumulation toxicity in OsPHR2overexpression and wild type plants by reducing Pi uptake, which in turn actives the increased expression of PSI (Phosphate Starvation Induced) genes in stagnant plants. Thus, when evaluating the Pi use efficiency of the rice germplasm or transgenic materials in hydroponic experiments, the impact of the low oxygen condition that occurs naturally in waterlogged paddies should be considered.Mutation of OsPH02exhibits delayed flowering time, due to the altered expression of flowering time genes OsHdl,OsHd3a and OsRFT1. The physical interaction between OsPHO2and OsGI provides a new cross-talk between Pi homeostasis and flowering time regulation. OsGI and OsPHO2involve in phosphate homeostasis in a photoperiod independent pathway.Pi remobilization from old to young leaves is impaired in both pho2and gi plants, resulting in Pi overaccumulation in the old leaves. Microarray analyses reveal that more than55%of the genes differentially expressed in gi plants are overlapping with the set of differentially expressed genes in pho2plants. It is seen that among overlapping genes in leaves, several functional categories including cell wall, phenylpropanoid metabolism and protein synthesis are over-represented. Sucrose transporters are suppressed in both pho2and gi leaves, indicating OsPHO2and OsGI may involve in flowering time regulation and Pi homeostasis via regulating sucrose transporters.In summary, this study investigated the impact of low oxygen on Pi uptake and the interaction between OsPHO2and OsGI protein, and identified the impact of root oxygen deficient stress and flowering time regulation gene on phosphate homeostasis in rice.