Screening Of Pi Response Mutants And The Molecular Mechanism Of The Plant Response To Pi Starvation Stress In Arabidopsis

Phosphorus(Pi)is one of the macronutrients required for plant growth and development.When grown under phosphate deficiency,plants undergo a series of physiological and biochemical responses to adapt to the environment and sustain growth.For Arabidopsis,responses to growth under phosphorus deficiency include inhibition of primary root growth,increased number of lateral roots and root hairs,increased acid phosphatase secretion,and decreased photosynthesis rate.Low temperature is one of the important environmental stress factors.Under low temperature stress,photosynthetic rate decreases,energy production and material synthesis are inhibited,respiration rate is increased,consumption is increased,the plants are in the state of starvation,which will affect the normal growth and development of plants,and may even cause the death of plants..Low temperature stress reduces the photosynthesis rate of plants,and phosphate deficiency also reduces the photosynthesis rate of plants.Iron(Fe)homeostasis is crucial for plants adaptation to aforesaid stresses,but,the underlying mechanism involved under combined stress condition was poorly understood until now.Here,we report that ALUMINUM ACTIVATED MALATE TRANSPORTER 1(ALMT1)and SENSITIVE TO PROTEIN RHIZOTOXICITY(STOP1)are modulators of Fe accumulation under combined action of Pi starvation and chilling stress.Iron uptake increased in the stem cell niche(SCN)of roots under phosphate deficiency and 4 ? treatment(P-4?)compared with P-23 ?.In contrast,almt1 and stop1 mutants exhibited lower iron concentrations compared to wild type.The RNA-seq analysis demonstrated that expression level of 48 photosynthetic genes in wild type roots increased under P-4 ? compared to P-23 ?.Moreover,almt1 and stop1 mutants displayed higher levels of expression of photosynthesis-related genes under P-4 ?,the average chloroplast number and starch granule number in the shoot apical meristems of almt1 and stop1 were lower than those of WT,and the plastids in roots were poorly developed under P-4 ?.Therefore,our results highlight the induction of photosynthetic gene expression and increased Fe accumulation by ALMT1 and STOP1 for plant adjustment to chilling stress in association with phosphate deficiency.In this work,we identified an Arabidopsis mutant,hypersensitive to Pi starvation20(hps20),which displayed increased sensitivity in Pi starvation responses.Expression level of Pi starvation-induced(PSI)genes in hps20 mutant was much higher than wild type(WT)plants under Pi deficiency.Production of acid phosphatase(APase)was also enhanced in hps20 mutant under Pi starvation.Furthermore,hps20 mutant accumulated more anthocyanin than WT when grown on Pi-deficient medium.RT-PCR analysis indicated that the phenotypes of hps20 mutant were caused by mutation within the TIP2(Gamma Tonoplast Intrinsic Protein 2)gene.The Pi content in the leaves of hps20 mutant was lower than that of the wild type,while it was higher in roots than in WT when grown under either Pi sufficiency or deficiency conditions,which is similar to the phenotype of the pho1 mutant.This indicates that TIP2 gene may participate in the Pi signal transduction process by regulating the transport of Pi in plants.