Comparative Study On The Pi Signal And Phytohormone Regulation Of OsIPS1 And OsIPS2 Genes Expression In Rice (Oryza Sativa L.)

A worldwide shortage of available phosphate (Pi) in soil has limited the growth and yield of crops .So it is very significant to study the plant stress responsible molecular mechanism under phosphate starvation and improve the genetic background of crops. With the analysis of ESTs from rice Nipponbare cDNA library screened by a method of Suppression subtracted hybridization (SSH), the phosphate-induced genes OsIPSl and OsIPS2 were cloned in this research. OsIPS2 has been reported as OsPIl by Wasaki et al. on 2003. To investigate the gene sequence characters of OsIPSl, OsIPS2 and expression pattern between them under different treatments, as well as a transgenic research, we concluded as following:1. By cloning the full-length gene of OsIPSl and analyzing the characters of the gene sequences and expressions of OsIPSl, OsIPS2, we confirmed that the two genes belong to TPSIl/Mt4 family. Moreover, with comparison of nucleic acid sequences, we found the homologous genes of OsIPSl, OsIPS2 in maize, wheat and Barley, which were named as ZmlPSl, ZmIPS2 (maize); TalPSl, TaIPS2 (wheat), HvIPSL HvIPS2 (barley) respectively. The analysis results suggest that it exists two subgroup I and II in TPSIl/Mt4 family. I subgroup includes the dicotyledon genes TPSI1, Mt4, At4, AtIPSI and the monocotyledon novel genes OsIPSl, ZmlPSl, TalPSl, HvIPSl, while II subgroup includes the novel genes OsIPS2, ZmIPS2, TaIPS2 and HvIPS2 which were found only in monocotyledon. The genes At4-l, At4-2 found in Arabidopsis recently don't belong to the above two subgroups.2. The expression pattern of rice OsIPSl and OsIPS2 under phosphate starvation:1) A temporal two-step expression involves the low transcriptional abundance induced during the early stage of P stress and the high transcriptional abundance during a continuous severe P stress. 2) Under P starvation condition, the expression of OsIPSl gene mainly locates on lateral roots and the stele of primary roots, but scarcely on shoots; OsIPS2 expression in roots is similar with OsIPSl, but much more in shoots than OsIPSl. 3)It exists two expression modes under P-starvation, namely the systemic up-regulation depending on the P status of whole plant and the local inducement due to the local P available of plantroots. The two modes are independent each other. Under the early stage of P stress, the local signal aroused by external P concentration varieties can regulate the genes expression rapidly; during the continuous severe P stress, systemic regulation is dominant while the local inducement still exists. 3. The effects of phytohormone on rice OsIPSl and OsIPS2 genes under the systemic and local regulation of P-starvation:Under both the systemic and local P-starvation, 1) exogenous auxins can enlarge the induced levels of OsIPSl and OsIPS2 to a certain extent; 2) exogenous cytokinins can repress the expression of OsIPSl and OsIPS2 remarkably; 3) exogenous ABA can depress the induced levels of OsIPSl and OsIPS2 to a certain extent; 4) exogenous ethylenes have no visible effects on the expressions of OsIPSl and OsIPS2.The above phytohormone can't induce the expressions of OsIPSl and OsIPS2 under normal nutrition conditions.4. Through the transform experiments in vivo, It suggests that the element P1BS is the P-starvation response binding site and the indispensable component for the drastic and specific inducement expression of gene OsIPSl by P-starvation.5. It doesn't exist the a functional positive regulatory feedback on the level of mRNA between OsIPSl and OslPS2.