Nicotiana benthamiana XYLEM CYSTEINE PROTEASE genes facilitate tracheary element formation in interfamily grafting

Grafting is a plant propagation technique widely used in agriculture.A recent discovery of the capability of interfamily grafting in Nicotiana has expanded the potential combinations of grafting.In this study,we showed that xylem connection is essential for the achievement of interfamily grafting and investigated the molecular basis of xylem formation at the graft junction.Transcriptome and gene network analyses revealed gene modules for tracheary element(TE)formation during grafting that include genes associated with xylem cell differentiation and immune response.The reliability of the drawn network was validated by examining the role of the Nicotiana benthamiana XYLEM CYSTEINE PROTEASE(NbXCP)genes in TE formation during interfamily grafting.Promoter activities of NbXCP1 and NbXCP2 genes were found in differentiating TE cells in the stem and callus tissues at the graft junction.Analysis of a Nbxcp1;Nbxcp2 loss-of-function mutant indicated that NbXCPs control the timing of de novo TE formation at the graft junction.Moreover,grafts of the NbXCP1 overexpressor increased the scion growth rate as well as the fruit size.Thus,we identified gene modules for TE formation at the graft boundary and demonstrated potential ways to enhance Nicotiana interfamily grafting.

ATP binding cassette proteins ABCG37 and ABCG33 function as potassium-independent cesium uptake carriers in Arabidopsis roots

Radiocesium accumulated in the soil by nuclear accidents is a major environmental concern.The transport process of cesium(Cs^(+))is tightly linked to the indispensable plant nutrient potassium(K^(+))as they both belong to the group I alkali metals with similar chemical properties.Most of the transporters that had been characterized to date as Cs*transporters are directly or indirectly linked to K^(+).Using a combinatorial approach of physiology,genetics,cell biology,and root uptake assay,here we identified two ATP-binding cassette(ABC)proteins,ABCG37 and ABCG33,as facilitators of Cs^(+)influx.A gain-of-function mutant of ABCG37(abcg37-1)showed increased sensitivity to Cs^(+)-induced root growth inhibition,while the double knockout mutant of ABCG33 and ABCG37(abcg33-1abcg37-2)showed resistance,whereas the single loss-of-function mutants of ABCG33 and ABCG37 did not show any alteration in Cs^(+)response.In planta short-term radioactive Cs^(+)-uptake assay along with growth and uptake assays in a heterologous system confirmed ABCG33 and ABCG37 as Cs^(+)-uptake carriers.Potassium response and content were unaffected in the double-mutant background and yeast cells lacking potassium-uptake carriers transformed with ABCG33 and ABCG37 failed to grow in the absence of K^(+),confirming that Cs^(+)uptake by ABCG33 and ABCG37 is independent of K^(+).Collectively,this work identified two ABC proteins as new Cs^(+)-influx carriers that act redundantly and independent of the K^(+)-uptake pathway.