Increased extensin levels in Arabidopsis affect inflorescence stem thickening and height

Extensins are hydroxyproline-rich glycoproteins which are abundant in the cell walls of higher plants and whose precise function has been the subject of much speculation. In order to investigate this, transgenic A. thaliana plants were generated containing the Arabidopsis Atext1 extensin coding sequence under the transcriptional control of the strong constitutive CaMV 35S promoter. Northern analysis and RT-PCR identified transgenics with high constitutive levels of Atext1 mRNA. Hydroxyproline assays confirmed that transgenic plants which over-expressed Atext1 contained high levels of hydroxyproline-rich protein. Phenotypic analysis of the transgenics showed that there were no significant phenotypic effects on the timing of different developmental stages or on the general form of the plant. However, transgenics with high extensin levels showed an enhanced increase in stem thickness, with an indirect effect on stem height. This effect, is, however, rather small, with a reduction in height of between 5-8% depending on the transgenic line being analysed.