Poster: Vegetative Development

Abs # 433: BSH1 and BSH2 two novel Arabidopsis genes affecting stem elongation and xylem fiber differentiation

Presenter:	Holmlund, Mattias , Mattias.Holmlund@genfys.slu.se
Authors	Holmlund, Mattias  (A)   Norberg, Mikael  (A)   Nilsson, Ove  (A)
Affiliations:	(A): Department of Forest Genetics and Plant Physiology

Here we describe the activation tagged bsh1 mutant a semidominant gain of function mutation of Arabidopsis caused by a T-DNA insertion of four enhancer elements from the constitutive active cauliflower mosaic virus 35S promoter, conferring a phenotype of dwarfism, reduced apical dominance and a shortened hypocotyl which is associated with a decreased epidermal cell elongation. The internal cell organisation and the differentation of secondary tissues in the hypocotyls are also affected. The cambium is partly disrupted by enlarged parenchyma cells and the onset of xylem fiber differentation has been delayed into late senecense. The position of the T-DNA insert together with the RNA analyses suggests that the mutant phenotype is caused by overexpression of a previously uncharacterised gene located adjacent to the enhancer elements, we call this gene BSH1. The BSH1 gene displays a high homology to another gene of unknown function, which we have named BSH2. Both genes contain a BTB/POZ domain and three ANK-repeats. These domains are involved in protein-protein interactions, suggesting that BSH1/BSH2 might be part of a lager protein complex. The expression of the BSH genes has been studied and the results indicates that BSH1 is expressed at a low level in hypocotyls, petioles and rosette stem, while BSH2 is abundantly expressed in all aerial tissues. These observations, together with the finding that BSH1 gets expressed in hypocotyl tissue at the onset of secondary growth, suggests that BSH1 might have a role in xylem fiber differentiation. We have recently identified a hybrid aspen (Populus tremula x tremuloides) homolog of the BSH-gene, called PttBSH. Based on these experiments we discuss the role of the BSH genes in the regulation of plant development and wood formation.