Expression of endoxyloglucan transferase genes in acaulis mutants of Arabidopsis

A mutant of Arabidopsis with reduced internodal cell length, acaulis5 (acl5 ), has recently been shown to have reduced transcript levels of a gene for endoxyloglucan transferase, EXGT-A1 (Y. Hanzawa, T. Takahashi, Y. Komeda [1 997] Plant J 12: 863-874). In the present study, we cloned genomic fragment s of five members of the EXGT gene family, EXGT-A1, EXGT-A3, EXGT-A4, XTR2, and XTR3, and examined their expression in the wild type and in a series o f acl mutants. In wild-type plants, the EXGT-A3 gene showed higher expressi on in lower internodes (internodes between nodes bearing axillary shoots) t han in upper and young internodes, in which EXGT-A1 was highly expressed. E XGT-A4 was preferentially expressed in roots and XTR3 in siliques. The XTR2 gene was constitutively expressed. In acl1, acl3, and acl4 mutants, which have a severe defect in leaf expansion as well as in internode elongation, the EXGT-A1 gene showed reduced levels of expression before bolting of plan ts. In contrast, XTR3 was increased in these mutant seedlings. Reduction of EXGT-A1 expression was also detected after bolting of all acl mutants exce pt acl2, whose growth defect is restricted to lower internodes. These resul ts suggest the involvement of each EXGT in different aspects of organ devel opment.