Study On Low Phosphate Adaptation Mechanisms Of Desert Shrub Zygophyllum Xanthoxylum

Phosphorus(P)is essential for the growth and development of plants.Because of water deficit,salt accumulation in surface soil and limited cation exchanges,P is one of the major limiting nutrients in desert areas.Zygophyllum xanthoxylum is a dominant species in desert area and has strong stress resistance.But its low-phosphorus adaptation mechanism has not yet been reported.In this study,Z.xanthoxylum was used as the material and processed with different P levels to study the relationship between P efficiencies and P homeostasis,and clarify the P redistribution strategy,research the photosynthetic process response to low phosphorus and its mechanism,through RNAseq to analyse the changes of genes and pathway involved in P absorption and P utilization.The researche provided basic information and new perspectives for understanding of the biological processes of desert plants adapting to low Pi environments,and generate important significance for the restoration of the ecological environment of desert areas and the genetic improvement of forages.The main conclusions are as follows:(1)Z.xanthoxylum had a high ability to absorb and utilize P.The desert plant Nitraria tangutorum was used as a control.The biomass,P concentrations and relative growth rates were proved have no significant differences in Z.xanthoxylum with increasing amounts of Pi;while the control plant Nitraria tangutorum showed upward trends;The P homeostasis of Z.xanthoxylum was higher than that of N.tangutorum,and P concentrations in all treatments were lower than in N.tangutorum,but C:P were higher than in N.tangutorum.It showed that Z.xanthoxylum had stronger P utilization capacity.The strong P efficiency,and high and stable dry matter accumulation,were likely contributors in maintaining homeostasis.(2)P deficiency treatment had no significant effect on the biomass of Z.xanthoxylum,but it changed its P reactivation and distribution.P deficiency caused a significant decrease in P distribution to mature leaves,and a significant increase in P distribution to roots and stems.P in mature leaves was reactivated and distributed to roots and stems as a result of P deficiency.When the supply of P was limited,Z.xanthoxylum can reactivate P in the body to ensure normal growth,but its aboveground transportation and distribution strategy was "stem priority" instead of "apical dominance".(3)P deficiency did not cause a significant reduce in photosynthetic indicators,and did not weaken the photosynthetic electron transport process.Under the 10 D and40D treatments,glycolipids contents increased significantly while phospholipids contents remained unchanged in the leaves.Under the 1D and 10 D treatments,Pi concentration and ATPase activity in the chloroplast were increased significantly,but there was no significant difference under 40 D treatment.Under P limitation,Z.xanthoxylum provided structural and functional protection for the electron transfer process by increasing glycolipids contents while maintaining phospholipids stability;at the same time,more Pi was distributed to the chloroplast,in order to enhance ATPase activity,and provided continuous and stable assimilation in the photosynthetic process.(4)We obtained 364,614 unigenes and 9,270 differentially expressed genes(DEGs)by transcriptome sequencing.The analysis of the DEGs revealed that 1)the genes related to external P absorption(PHT1s)and internal phosphorus transport(PHO1s,PHT2 s and TPTs)were up-regulated by P deficiency,which was conducive to absorption of external phosphorus and the redistribution of internal phosphorus in Z.xanthoxylum;2)the key genes for organic acid synthesis related to the activation of poorly soluble phosphorus in the soil were only up-regulated under 1D treatment,but the acid phosphatase and ribonuclease encoding genes related to the reactivation of organic phosphorus in vivo and in vitro were mainly up-regulated under 10 D treatment,this methods helped Z.xanthoxylum improve P efficiencies;3)genes involved in phospholipids synthesis were not differentially expressed,but genes involved in phospholipids metabolism were down-regulated and genes related to glyceroglycolipids synthesis were up-regulated,indicating that Z.xanthoxylum had a special way of membrane lipid remodeling;4)the up-regulated expression of genes involved in encoding proteins related to the photosynthetic process were induced by P deficiency,indicating that low phosphorus stress did not inhibit the photosynthetic process and ensured the stability of biomass of Z.xanthoxylum.