Study On Regulation Of Alkaline-stress Resistance By ABC1K1 In Arabidopsis

Alkaline stress is one of the most important environmental factors,which limits crop growth,development and productivity.Under alkaline condition,some trace elements,such as Fe,Cu,Mn,are formed insoluble compounds,causing the deficiency of these trace elements.Among these trace elements,the deficiency of Fe is a most important factor under alkaline condition.Plant can secrete proton from root to acidize alkaline soil and up-regulate the expression of iron transport relative genes,such as FR02 and IRT,to promote iron absorption.However,it is not very clear how iron transport is involved in response to alkaline stress and what mechanisms control this process.In order to identify genes that are involved in the response to alkaline stress in Arabidopsis,we screened an Arabidopsis T-DNA activation-tagged pool and isolated a high-pH-sensitive mutant,1428.On alkaline medium or in alkaline soil,the seedlings of the mutant are paler and smaller than that of wild type.The T-DNA insertion site in 1428 mutant is identified by thermal asymmetric interlaced(TAIL)-PCR and sequence,which localizes in the seventh exon of At4g31390,which encodes ABC1K1,a number of the ABC1 protein kinase family.Hence,we renamed the mutant as abclkl-3.Over-expression of ABC1K1 increases plant alkaline tolerance.ABC1K1 is localized only in chloroplast,at both the membrane and stroma of the chloroplast.The abclkl-3 mutant loses most of the starch grains and displays discontinuous thylakoids membranes under high pH condition.Both the gene expression and kinase activity of ABC1K1 are induced by alkaline stress,indicating that ABC1K1 is involved in the response to alkaline stress.The abclkl mutant is also sensitive to the deficient of iron.The phenotype of abclkl becomes more obvious with the decrease of iron concentration in the medium,and applying external soluble iron Fe-EDDHA in the high pH medium can partially rescue the phenotype of abc1kl1 leading a conclusion that the phenotype of abclkl under alkaline condition is at least partially caused by iron deficiency.Further measurements show that the iron content and the expression of key iron transportation genes are reduced in abc1k1 mutant than that in Col-0 under alkaline condition.Our observations also suggest that deficiency of iron in abclkl mutant leads to accumulate ROS in chloroplast.Considering that ABC1K1 localizes at the chloroplasts but the key iron transportation genes are expressed in roots,we analyze if the restrain retrograde signal of chloroplast plays a role in this regulation.The inhibitor,Norfluzon(NF),of the restrain retrograde signal suppresses the expression of iron transporting genes in roots.Glutathione content is significant reduced in abclkl mutant compared with wild type.Addition of external reductive glutathione can rescue the phenotype of abclkl under alkaline stress and the suppression of the expression of iron transporting genes by NF.Therefore,the glutathione may function as a signal between the chloroplast and iron transporting gene expression in response to the alkaline stress.In this study,we demonstrate that the chloroplast kinase ABC1K1 is required for regulation of alkaline-stress resistance in Arabidopsis.Under alkaline condition,ABC1K1 is involved in regulation iron transportation in roots.Glutathione,regulated by kinase ABC1K1,may work as a potential signal molecule to connect chloroplast and iron transportation.