Expression of genes involved in adaptation to low phosphorus in nodules of two symbiotic associations of chickpea-Mesorhizobium

Crop production of important legumes such as chickpea is often limited by low phosphorus (P) in soils. This limitation that is mainly attributed to inhibition of nodule activity and consequently decline in nitrogen fixation under P deficiency. Therefore, the precise identification of molecular mechanisms responsible for improvement of symbiotic effectiveness of symbiotic associations of legume-rhizobium can be used to enhance productivity through genetic engineering and breeding methods. In this study, changes in expression level of some genes in nodules of two symbiotic associations (chickpea-M. mediterraneum SWRI9 and chickpea-M. ciceri CP-31) under P starvation were investigated by Real-time PCR. Based on the results obtained from thegrowth parameters and Pi content in nodules and roots, the two examinedstrains of rhizobia differ markedly in tolerance to phosphorus deficiency.chickpea-M. mediterraneum SWRI9 was a P deficiency sensitive symbiotic associations and chickpea-M. ciceri CP-31 was much more tolerant one to P deficiency. Under P deficiency, the expression level of inorganic phosphate transporter 1-4like, inorganic phosphatase 2-like and malate dehydrogenase genes in nodules chickpea-M. ciceri CP-31 increased as compared their expression under P-sufficient conditions. In both symbiotic associations, the expression level of Phosphate transporter 1 in nodules decreased under P deficiency. In addition, the expression level of histidin kinase genes increased in nodules of chickpea-M. mediterraneum SWRI9 in response to P deficiency. Different response of symbiotic effectiveness to P deficiency in two symbiotic associations is related to difference in expression level of studied genes.