Preliminary Study On The Function Of Arabidopsis Receptor-like Kinase R235 In Response To Iron Deficiency

Iron is one of the most abundant metal elements in the earth's crust,and is necessary for plant growth and development,playing a vital role in life processes such as photosynthesis,hormone synthesis,mitochondrial respiration,and nitrogen assimilation.However,most of the iron in the soil exists in the form of mineral or insoluble compounds that are difficult for plants to use effectively.Dicotyledonous and non-grainaceous monocotyledonous plants absorb iron from the soil through mechanism I,which includes three steps:proton efflux,Fe³⁺reduction and Fe²⁺transport.In Arabidopsis thaliana,the reduction of Fe³⁺that is catalyzed by the ferric reductase FRO2 is most important,and is considered to be the rate-limiting step of the entire iron absorption process.Nevertheless,how FRO2 regulated remains elusive.Upon screening the T-DNA insertion mutant library of Arabidopsis Receptor-like kinases(RLKs)for iron deficiency response,we identified an r235 loss-of-function mutant that is more tolerant to iron deficiency than wild type(WT).The analysis of R235 transgenic complementation lines and overexpressors confirmed that lack of R235 leads to increased tolerance to iron deficiency.Quantitative Real-time PCR showed that the expression of iron deficiency-responsive genes in the r235 mutant was higher than WT under iron deficiency,indicating that R235 may negatively regulates the iron deficiency response to modulate iron homeostasis in Arabidopsis.Further measurements of ferric reductase(FCR)activity and iron content showed that r235 mutant exhibited much higher FCR activity and accumulated more iron in both the roots and shoots when exposed to iron deficiency,suggesting that R235 may affect the Arabidopsis iron uptake efficiency via regulation of FRO2 activity under iron deficiency.Through Bimolecule Fluorescence Complementary experiments,we found that the kinase domain of R235 interacted with the C-terminus of FRO2,indicating that R235 may directly regulate the FRO2 activity.Together,these preliminary results indicate that R235 may negatively regulate the Arabidopsis iron uptake process via inhibiting FRO2 activity and/or FRO2 expression.