Pollen tubes of Nicotiana alata express two genes from different beta-glucan synthase families

The walls deposited by growing pollen tubes contain two types of P-glucan, the (1,3)-beta -glucan callose and the (1, 4)-beta -glucan cellulose, as we ll as various a-linked pectic polysaccharides. Pollen tubes of Nicotiana al ata Link et Otto, an ornamental tobacco, were therefore used to identify ge nes potentially encoding catalytic subunits of the callose synthase and cel lulose synthase enzymes. Reverse transcriptase-polymerase chain reactions ( RT-PCR) with pollen-tube RNA and primers designed to conserved regions of b acterial and plant cellulose synthase (CesA) genes amplified a fragment tha t corresponded to an abundantly expressed cellulose-synthase-like gene name d NaCslD1. A fragment from a true CesA gene (NaCesA1) was also amplified, b ut corresponding cDNAs could not be identified in a pollen-tube library, co nsistent with the very low level of expression of the NaCesA1 gene. RT-PCR with pollen-tube RNA and primers designed to regions conserved between the fungal FKS genes [that encode (1,3)-beta -glucan synthases] and their presu med plant homologs (the Gsl or glucan-synthase-like genes) amplified a frag ment that corresponded to an abundantly expressed gene named NaGsl1. A seco nd Gsl gene detected by RT-PCR (NaGsl2) was expressed at low levels in imma ture floral organs. The structure of full-length cDNAs of NaCslD1, NaCesA1, and NaGsl1 are presented. Both NaCslD1 and NaGsl1 are predominantly expres sed in the male gametophyte (developing and mature pollen and growing polle n tubes), and we propose that they encode the catalytic subunits of two P-g lucan synthases involved in pollen-tube wall synthesis. Different P-glucans deposited in one cell type may therefore be synthesized by enzymes from di fferent gene families.