Regulation of inositol 1,2,4,5,6-pentakisphosphate and inositol hexakisphosphate levels in Gossypium hirsutum by IPK1.

The IPK1 genes, which code for 2-kinases that can synthesize Ins(1,2,4,5,6)P from Ins(1,4,5,6)P, are expressed throughout cotton plants, resulting in the highest Ins(1,2,4,5,6)P concentrations in young leaves and flower buds. Cotton leaves contain large amounts of Ins(1,2,4,5,6)P and InsP compared to plants not in the Malvaceae family. The inositol polyphosphate pathway has been linked to stress tolerance in numerous plant species. Accordingly, we sought to determine why cotton and other Malvaceae have such high levels of these inositol phosphates. We have quantified the levels of InsP and InsP in different tissues of cotton plants and determined the expression of IPK1 (inositol 1,3,4,5,6-pentakisphosphate 2-kinase gene) in vegetative and reproductive tissues. Gossypium hirsutum was found to contain four IPK1 genes that were grouped into two pair (AB, CD) where each pair consists of very similar sequences that were measured together. More IPK1AB is expressed in leaves than in roots, whereas more IPK1CD is expressed in roots than in leaves. Leaves and flower buds have more InsP and InsP than stems and roots. Leaves and roots contain more InsP than InsP, whereas flower buds and stems contain more InsP than InsP. Dark-grown seedlings contain more InsP and InsP than those grown under lights, and the ratio of InsP to InsP is greater in the light-grown seedlings. During 35 days of the life cycle of the third true leaf, InsP and InsP gradually decreased by more than 50%. Silencing IPK1AB and IPK1CD with Cotton Leaf Crumple Virus-induced gene silencing (VIGS) resulted in plants with an intense viral phenotype, reduced IPK1AB expression and lowered amounts of InsP. The results are consistent with Ins(1,2,4,5,6)P synthesis from Ins(1,4,5,6)P by IPK1. This study detailed the central role of IPK1 in cotton inositol polyphosphate metabolism, which has potential to be harnessed to improve the resistance of plants to different kinds of stress.