Inositol phosphates’ synthesis in pea Pisum sativum L. root seedlings at the early stages after Rhizobium leguminosarum bv. viciae inoculation

Studying the role of inositol phosphates in the regulation of signal exchange between leguminous plants and nodule bacteria is of great interest since it affects the regulation of calcium level in the root cells in response to bacterial signals during symbiosis development. The regulation of intracellular calcium content is one of the key events in the control of symbiosis development, but remains very poorly understood. In present work, we revealed a significant increase in the content of inositol hexasphosphate (IP6), which occurs in response to the recognition of Nod factors and indicates that in plants, unlike animals, this form (along with the inositol triphosphate (IP3)) may be important for signal transduction. This is consistent with the data that receptor for IP3 in plants has not yet been found, despite numerous efforts. Expression analysis of the genes encoding enzymes of two biosynthetic pathways for inositol phosphates showed stimulation of the PsITPK1 gene (Psat6g210960), which can control the phospholipid-independent pathway for synthesis of these compounds. Despite the fact that PsPIP5K (Psat5g134320) important for another pathway did not show increased expression in our experiments upon inoculation, the activation of the phospholipid-dependent pathway of inositol phosphate biosynthesis can be evidenced by stimulation of a number of genes encoding pospholipases C (PLCs) which were previously found in pea Pisum sativum as well as during analysis of transcriptome of Medicago truncatula root treated with Nod factors. Therefore, in plants, in contrast to animals, the pathways for the synthesis of inositol phosphates can be more diverse, which indicates the plasticity of signal pathways.