An Arabidopsis protein with a novel calcium-binding repeat sequence interacts with TONSOKU/MGOUN3/BRUSHY1 involved in meristem maintenance.

TONSOKU(TSK)/MGOUN3/BRUSHY1 from Arabidopsis thaliana, which plays an important role in the maintenance of meristem organization, contains an LGN repeat motif similar to that found in animal proteins involved in asymmetric cell division. One protein that interacts with the LGN motif of TSK in a yeast two-hybrid screen, TSK-associating protein 1 (TSA1), contains a 10-fold repeat of a unique 41 amino acid sequence. The repeat sequence, with a glutamic acid-phenylalanine-glutamic acid (EFE) conserved core sequence, is enriched with acidic amino acids.

TONSOKU is expressed in S phase of the cell cycle and its defect delays cell cycle progression in Arabidopsis.

TONSOKU(TSK)/MGOUN3/BRUSHY1 of Arabidopsis thaliana encodes a nuclear leucine-glycine-aspargine (LGN) domain protein implicated to be involved in genome maintenance, and mutants with defects in TSK show a fasciated stem with disorganized meristem structures. We identified a homolog of TSK from tobacco BY-2 cells (NtTSK), which showed high sequence conservation both in the LGN domain and in leucine-rich repeats with AtTSK. The NtTSK gene was expressed during S phase of the cell cycle in tobacco BY-2 cells highly synchronized for cell division.

A novel Arabidopsis gene TONSOKU is required for proper cell arrangement in root and shoot apical meristems.

Root apical meristem (RAM) and shoot apical meristem (SAM) are vital for the correct development of the plant. The direction, frequency, and timing of cell division must be tightly controlled in meristems. Here, we isolated new Arabidopsis mutants with shorter roots and fasciated stems.