Identification of the Causative Genes of Calcium Deficiency Disorders in Horticulture Crops: A Systematic Review

The occurrence of calcium (Ca2+) deficiency disorders is a severe problem in the production of horticulture crops. Recently, several studies have investigated the role of gene expression in Ca2+ deficiency disorders and/or Ca2+ accumulation, providing an indication of the mechanism of Ca2+ deficiency disorders at the genetic level. To determine the relation between gene expression and the occurrence of Ca2+ deficiency disorders, we conducted a systematic review of the literature using the Preferred Reporting Items for Systematic Reviews and Meta-analyses protocol. In our initial search, we extracted studies investigating the relationships between Ca2+ deficiency disorders (tipburn and blossom-end rot) and gene expression. In our second search, we extracted studies involving functional analyses of the genes associated with Ca2+ deficiency and/or Ca2+ accumulation in plant organs. Thirty-seven articles were extracted from both searches. Studies on Ca2+ movement-related genes (Ca2+ antiporters, calreticulin, Ca2+ pumps, Ca2+ channels, and pectin methylesterases) accounted for the majority of these articles. Particularly, the effects of the expression of CAXs (Ca2+/H+ antiporters) and CRT (calreticulin) on the occurrence of Ca2+ deficiency disorders were demonstrated in studies extracted from both searches. Further research focusing on these genes may reveal the causative genes for Ca deficiency disorders in different horticulture crops. We hope that the knowledge synthesized in this systematic review will contribute to the accumulation of further knowledge and elucidation of the causes of Ca2+ deficiency disorders