BcSKS11, a SKS gene from pollinated pistils of Chinese cabbage pak choi, is expressed continuously during the male gametophyte development, pollen germination and pollen-tube growth processes

Abstract

Cell wall-related genes and proteins are crucial for fertilisation-related events such as pollen germination and pollen-tube growth. Recent studies have focussed on the molecular mechanism of cell-wall synthesis and regulation of these processes; however, limited information is available on the mechanism and modification of the crucial cell-wall materials. We isolated a gene that is potentially involved in cell-wall metabolism from pollinated pistils of the male sterile line ‘Bcajh97-A’ in Chinese cabbage pak choi (Brassica campestris SKewed5 Similar 11, BcSKS11). BcSKS11 has several features of SKewed5 Similar (SKS) proteins, which are structures that are similar to plant multicopper oxidase but lack the 10 necessary residues of two copper-binding sites. A phylogenetic tree constructed from 49 SKS proteins found four clades, with BcSKS11 being in a clade with tobacco sequences. Reverse transcription–polymerase chain reaction and in situ hybridisation revealed that BcSKS11 was specifically expressed in uninucleate microspores, mature pollen grains and growing pollen tubes of pollinated pistils. These results suggest that BcSKS11 might be stored in mature pollen grains, in preparation for pollen germination and pollen-tube growth.