Arabidopsis brassinosteroid biosynthetic mutant dwarf7-1exhibits slower rates of cell division and shoot induction

Abstract

AbstractBackgroundPlant growth depends on both cell division and cell expansion. Plant hormones, including brassinosteroids (BRs), are central to the control of these two cellular processes. Despite clear evidence that BRs regulate cell elongation, their roles in cell division have remained elusive.ResultsHere, we report results emphasizing the importance of BRs in cell division. An Arabidopsis BR biosynthetic mutant,dwarf7-1, displayed various characteristics attributable to slower cell division rates. We found that theDWARF4gene which encodes for an enzyme catalyzing a rate-determining step in the BR biosynthetic pathways, is highly expressed in the actively dividing callus, suggesting that BR biosynthesis is necessary for dividing cells. Furthermore,dwf7-1showed noticeably slower rates of callus growth and shoot induction relative to wild-type control. Flow cytometric analyses of the nuclei derived from either calli or intact roots revealed that the cell division index, which was represented as the ratio of cells at the G2/M vs. G1 phases, was smaller indwf7-1plants. Finally, we found that the expression levels of the genes involved in cell division and shoot induction, such asPROLIFERATING CELL NUCLEAR ANTIGEN2(PCNA2) andENHANCER OF SHOOT REGENERATION2(ESR2), were also lower indwf7-1as compared with wild type.ConclusionsTaken together, results of callus induction, shoot regeneration, flow cytometry, and semi-quantitative RT-PCR analysis suggest that BRs play important roles in both cell division and cell differentiation in Arabidopsis.