What are the key mechanisms that alter the morphology of stigmatic papillae in Arabidopsis thaliana?

Pollination is one of the critical processes that determines crop yield and quality. Thus, it is an urgent need to elucidate the mechanisms underlying pollination. Our previous research has revealed a novel phenomenon that pollen attachment to stigma caused stigma shrinkage, whereas failure of pollen attachment to stigma due to the environmental stress induced elongation of stigmatic papillae. However, little is known about the mechanisms of these morphological alterations in stigmatic papillae. Since the RLK-ROPGEF-ROP network is a common mechanism for the elongation of pollen tubes and root hairs, this network may be also involved in the elongation of papillae in the stigma. In this review, we will discuss the known mechanisms regulating pollen tube growth and root hair elongation and attempt to propose an elongation mechanism of stigmatic papillae. In addition, we will suggest that the degradation of F-actin by a significant increase in Ca2+ induced by the components of pollen coat might be a putative molecular mechanism of stigmatic papillae shrinkage during pollen adhesion.