An investigation of the A6 beta-1, 3-glucanase gene family in Arabidopsis thaliana

The A6 gene family represents a distinct class of P-l,3-glucanase enzymes in higher plants (Hird et al., 1993). The genes differ from other known P-l,3-glucanases in both sequence characteristics and expression pattern. The DNA sequences encode proteins with a distinctive GINYG N-terminal motif and a long C-terminal extension. The A6 gene shows tapetum-specific expression, with maximum activity detected at the time of microspore release (Hird et al., 1993). The expression pattern of A6 suggests that this gene may be part of the callase enzyme complex required for the dissolution of the callose wall surrounding the tetrads of developing microspores within the anther (Hird et al., 1993). The preliminary work on the A6 gene family identified four anther-specific cDNAs from Brassica napus (Scott et al., 1991 Hird et al., 1993). As a continuation of this work, five A6 family genes have now been cloned and sequenced in Arabidopsis thaliana. All five are single copy genes, and the three genes that have been mapped to the Arabidopsis genome are located at unlinked positions on two different chromosomes. Analysis of the cDNAs corresponding to the A6 family genes has revealed considerable variation in expression pattern. Two of the A6 family genes show anther-specific expression, and three genes are constitutively expressed, indicating differential regulatory mechanisms for these genes. Two populations of T-DNA-tagged lines were screened for four of the Arabidopsis A6 family members in attempt to obtain lines carrying mutations in these genes, which may reveal more information on their biological function(s). One positive line was identified and later shown to contain an insertion At-A6 gene. Detailed analysis of this line showed that although the At-A6 transcript in the mutant line is shorter than wild type and does contain part of the T-DNA sequence, the hybrid mRNA is stable. No phenotype could be associated with the T-DNA insertion in At-A6.