| The alteration of root architecture is one of strategies of plant response to phosphate(Pi) starvation.Phosphate starvation inhibits primary root(PR) elongation and enhances lateral roots(LR) and root hairs(RH) in Arabidopsis.Interaction of Cytokinin(CTKs) signaling with Pi-starvation signaling has been demonstrated,while the effect of the interaction on root development is still unclear.In this study,we isolate two allelic Arabidopsis mutants with hypersensitive to both Pi-starvation and exogenous CTK(designated as cks1:cytokinin sensitive 1).Physiological and molecular characterizations of the mutant provide the following conclusions:1.Under Pi-starvation,the root cell elongation of cks1 mutants was inhibited at one day after germination(DAG).The cks1 mutants lost root meristem activity at earlier stage.The PR length of cks1 mutants was shorter than that of the wild type(WT).The reduced meristem zone size and abbreviated epidermal cell were found in the mutants..2.The endogenous CTKs concentration of cks1 mutants was reduced and the expression of genes involved in CTK biosynthesis and signaling were repressed in the mutants.3.The phosphate concentration(Pi) of cks1 mutants was not decreased in shoots and roots compared with WT under Pi-starvation.While treated with analog of phosphate,Phosphite,the PR growth of cks1 was similar with WT,suggesting that the supersensitive to Pi-starvation of the mutants is mediated by Pi-starvation signaling. The reduced expression levels of PSI genes(Phosphate starvation induced) in the mutants under Pi-starvation condition support the suggestion.4.T-DNA insertion sites were detected in the two mutants.In cks1-1 mutant,The T-DNA was inserted at the promoter region of the gene(At2g22300) which for a CaM-binding transcriptional activator(AtCMTA3).The T-DNA was inserted at tenth exon of AtCMTA3 in cks1-2 mutant.Map based cloning and complementation test confirm that the mutant phenotypes under Pi-starvation is caused by the T-DNA target gene,AtCMTA3.
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