Brassinosteroids, microtubules and cell elongation in Arabidopsis thaliana . II. Effects of brassinosteroids on microtubules and cell elongation in the bul1 mutant

Abstract

In order to elucidate the involvement of brassinosteroids in the cell elongation process leading to normal plant morphology, indirect immunofluorescence and molecular techniques were use to study the expression of tubulin genes in the bul1-1 dwarf mutant of Arabidopsis thaliana (L.) Heynh., the characteristics of which are reported in this issue (M. Catterou et al., 2001). Microtubules were studied specifically in the regions of the mutant plant where the elongation zone is suppressed (hypocotyls and petioles), making the reduction in cell elongation evident. Indirect immunofluorescence of alpha-tubulin revealed that very few microtubules were present in mutant cells, resulting in the total lack of the parallel microtubule organization that is typical of elongating cells in the wild type. After brassinosteroid treatment, microtubules reorganized and became correctly oriented, suggesting the involvement of brassinosteroids in microtubule organization. Molecular analyses showed that the microtubule reorganization observed in brassinosteroid-treated bul1-1 plants did not result either from an activation of tubulin gene expression, or from an increase in tubulin content, suggesting that a brassinosteroid-responsive pathway exists which allows microtubule nucleation/organization and cell elongation without activation of tubulin gene expression.

Gene Expression Profiling in Response to Ultraviolet Radiation in Maize Genotypes with Varying Flavonoid Content

“…The high level of these transcripts could be an indirect effect after DNA damage caused by UV-B radiation. Interestingly, transcripts for highly abundant proteins that vary during the cell cycle including cytoskeletal proteins such as actins, tubulins, and ankyrins (Klessig et al, 2000;Catterou et al, 2001); thioredoxin h (Marty et al, 1993); proteins participating in ubiquitin-mediated protein degradation such as cdc20, ubiquitin, proteosome proteins, and cyclins (Mironov et al, 1999;Kramer et al, 2000); and S-adenosylhomo-Cys hydrolase and argininosuccinato synthase (Coller et al, 2000) are all up-regulated by UV-B in our experiments. Furthermore, cell cycle regulatory proteins are elevated, which may reflect tighter control of cell division when leaf cells incur DNA damage from UV-B radiation.…”

TheArabidopsis lue1mutant defines a katanin p60 ortholog involved in hormonal control of microtubule orientation during cell growth

“…This effect suggests that AtKSS and/or other MT-associated proteins indirectly affect GA feedback via regulatory pathways to integrate cytoskeletal organization and cell elongation. Although such pathways remain obscure, they may include signaling pathways related to brassinosteroids that also affect MT organization (Catterou et al, 2001) and that we have shown to increase the expression of AtGA20ox1 .…”

A Proteomics Study of Brassinosteroid Response in Arabidopsis

“…Interestingly different actin and tubulin genes, ACT11, TUB1, and TUB8, showed BR-induced expression in previous microarray studies (24). Our finding that several tubulin genes were BR-induced is particularly interesting in light of studies of the BR-deficient mutant bul1, which exhibits defects in microtubule organization that can be rescued by BR treatment (81).…”