Role of calcium in the expression of MAP kinase kinases (MKKs) and MAP kinases in tomato flower abscission
The mitogen activated protein kinase (MAPK) cascade is an important intracellular signaling module that functions as a convergent point for crosstalk during stress signaling. In this study, we constructed a phylogenetic tree for MAP kinase kinases (MKKs) and MAP kinases (MPKs) in Arabidopsis and Lycopersicon esculentum (tomato) and found that abscission-related AtMKK4 and AtMKK5, and AtMPK3 and AtMPK6 clustered with LeMKK2, and LeMPK1,and LeMPK2 and LeMPK3, respectively. To investigate whether there was a link between homology and abscission, we studied all the LeMKKs at the messenger ribonucleic acid (mRNA) transcript level. LeMKK2 and its homologue AtMKK4/5 both have roles in regulating abscission. Quantitative real time polymerase chain recation (qRT-PCR) of LeMPK1 and LeMPK2, which are highly homologous to AtMPK3 and AtMPK6, most probably mediate abscission downstream through LeMKK2. Calcium depressed the expression of these genes in the early stages of abscission. Treatment with W7 (a calmodulin inhibitor) indicated that the expression of LeMKKs and LeMPKs depended on calmodulin during tomato flower explant abscission.
Keyword: Abscission, calcium, qRT-PCR, MAPK, tomato