Resolving the green branch of life: Current progress and future challenges
Nishiyama, Tomoaki , Sakakibara, Keiko , Hasebe, Mitsuyasu .
Evolution of meristem in land plants..
In vascular plant sporophytes, the shoot apical meristem repeatedly forms stem and lateral organs, such as leaves. However, the evolutionary origin of shoot apical meristem has been a mystery. The
sporophyte of bryophytes forms a single sporangium without lateral organs. However, some bryophytes, mosses and leafy liverworts, form leafy shoots in the gametophyte generation. We ask whether homologues of vascular plant genes involved in shoot apical meristem formation are involved in sporophyte development of bryophytes. We also examine whether homologous genes are involved in the gametophytic and sporophytic shoots. Molecular genetic studies in Arabidopsis thaliana revealed several genes involved in the formation and maintenance of the shoot apical meristem. SHOOT MERISTEMLESS is one such gene and is a member of the KNOX class 1 group of homeobox gene superfamilies. We investigated the expression patterns of class 1 KNOX genes in a moss, Physcomitrella patens. The expression of class 1 KNOX genes was detected in egg cells and young sporophytes, but not in gametophores (leafy shoots), suggesting that the moss class 1 KNOX genes are involved in sporophyte development but not in gametophytic shoots. Our analysis of 51 protein-coding chloroplast genes indicates that bryophytes are monophyletic with hornworts basal within bryophytes. This implies that class 1 KNOX genes were involved in sporophyte development in the last common ancestor of extant land plants. Differences in the regulation of KNOX genes might explain why vascular plants form shoots but bryophytes do not. Differences in the sporophyte architecture in bryophytes may also be explained by modification in the length of the meristem activity.
1 - National Institute for Basic Biology, Okazaki, 444-8585, Japan
Presentation Type: Symposium
Location: Ballroom 3 (Cliff Lodge)
Date: Wednesday, August 4th, 2004
Time: 10:45 AM