Downregulation of the mitogen-activated protein kinase SlMAPK7 gene results in pollen abortion in tomato

Abstract

Mitogen-activated protein kinases (MAPKs) play important roles in various aspects including plant development and stress response. The biological role of MAPKs in tomato development remains unclear. Here, multiple stable transgenetic lines were developed using either gene overexpression or RNA interference (RNAi) technology to investigate the role of SlMAPK7 in tomato reproductive development. Either upregulation or downregulation of SlMAPK7 did not drastically disturb the vegetative growth of tomato. However, in RNAi-based gene silencing plants, approximately 90 % of the pollen grains were identified to be abnormal and lack viability, which were malformed or collapsed. Cytological observations showed that anthers could develop normal microspore mother cells, but the uninucleate microspores failed to form normal mature pollen grains. Transmission electron microscopy examination demonstrated that accelerated degradation of tapetum occurred in the anther and finally the intine layer of pollen appears abnormal. In addition, although inhibition of SlMAPK7 gene did not alter fruit morphology, seed number in RNAi fruits was markedly reduced. Thus, the results demonstrated that SlMAPK7 is involved in tomato pollen development, possibly via regulation the degradation of tapetum.