Arabidopsis inositol 1,3,4-trisphosphate 5/6 kinase 2 is required for seed coat development.

Inositol 1,3,4-trisphosphate 5/6 kinase (ITPK) phosphorylates inositol 1,3,4-trisphosphate to form inositol 1,3,4,5-tetrakisphosphate and inositol 1,3,4,6-tetrakisphosphate which can be finally transferred to inositol hexaphosphate (IP₆) and play important roles during plant growth and development. There are 4 putative ITPK members in Arabidopsis. Expression pattern analysis showed that ITPK2 is constitutively expressed in various tissues. A T-DNA knockout mutant of ITPK2 was identified and scanning electron microscopy (SEM) analysis showed that the epidermis structure of seed coat was irregularly formed in seeds of itpk2-1 mutant, resulting in the increased permeability of seed coat to tetrazolium salts. Further analysis by gas chromatography coupled with mass spectrometry of lipid polyester monomers in cell wall confirmed a dramatic decrease in composition of suberin and cutin, which relate to the permeability of seed coat and the formation of which is accompanied with seed coat development. These results indicate that ITPK2 plays an essential role in seed coat development and lipid polyester barrier formation.