Ethylene Is Involved In Iron Deficiency Responses Of Rice Roots

Iron(Fe) is an essential nutrient for plant growth.Although it is abundant in soil,the availability to plants is low in soils.To cope with the limit of Fe supply,plants have evolved a complex set of physiological and developmental processes,which are under precise control of local and systematical signaling pathways.Therefore,elucidating the mechanism of signal regulation is of important for the improvement of plant tolerance to nutrient stress.There are two strategies for plants to cope with Fe deficiency stress.In Strategyâ… plants,Fe limitation invokes ethylene production,which in turn, regulates Fe deficiency responses.In contrast,ethylene is not involved in Fe-deficiency response in Strategyâ…¡plants.Oryza sativa(rice) is the only graminaceous plant that possessed a Strategyâ… -like system for iron uptake as well as the classic Strategyâ…¡system.Analysis of ethylene production in rice under Fe depletion indicated that ethylene production of rice root was significantly increased.Moreover,1-aminocyclopropane-1-carboxylic acid (ACC) treatment,a precursor of ethylene,conferred tolerance to Fe deficiency in rice by increasing internal Fe availability.Gene expression analysis of OsIRO2,OsIRT1,OsYSL15,OsNAS1 and OsNAS2 indicated that ethylene may regulate both Fe(â…¡) and Fe(â…¢)-phytosiderophore uptake systems.We further showed that the ethylene enhanced expressions of OsYSL15,OsNAS1 and OsNAS2 are dependent on the transcription factor OsIRO2.Under similar conditions no ethylene production or changes in gene expression were observed in Hoedeum vulgare L.(barley).Therefore, rice may activate ethylene production and signaling pathway under Fe limitation conditions and may be the only graminaceous plant that uses this pathway.P deficiency repressed ethylene production in rice.The inhibition of ethylene production by P deficiency could not be reversed by re-supplying of P.Besides,the expression of ethylene synthesis related genes was not repressed by P deficiency.These results imply that P limitation may have an indirect effect on ethylene production.Further analysis showed that the expression of the OsSAMS2 and OsARD1 genes that are involved in methionine cycle was repressed by P deficiency.Thus,the inhibition of ethylene production by P deficiency may be caused by the reduction of subtracts of ethylene production,which are the products of methionine cycle.