Light Regulation of β-Tubulin Gene Expression during Internode Development in Soybean (Glycine max [L.] Merr.)

Abstract

The relationship between tubulin gene expression and cell elongation was explored in developing internodes of Glycine max (L.) Merr., using light as a variable to alter the rate of elongation. Illumination of 10-day-old etiolated seedlings not only stopped first internode elongation, but also brought about a 80% decrease in the steady state level of ,-tubulin mRNA over the course of the subsequent 12 hours. This strong down regulation of j6-tubulin mRNA occurred without significant changes in the size of the soluble tubulin pool and it was accompanied by a marked increase in chlorophyll a/b binding protein mRNA.cases, the tubulin dimer pool is maintained through both transcriptional and post-transcriptional control of tubulin gene expression (1,17). Little is known about the regulation of tubulin synthesis in plants, but Cyr et al. (8) observed changes of several fold in the levels of tubulin protein and mRNA during carrot somatic embryogenesis. Furthermore, Fukuda (11) reported that the rate of tubulin synthesis increased during the formation of cortical microtubules in differentiating tracheary elements. The involvement of cortical microtubules in cell elongation and the increase in tubulin levels and in microtubule assembly which has been shown to accompany cell elongation (9, 29), make elongating tissues attractive as systems for investigating the regulation oftubulin synthesis in higher plants. Here, we show that changes in ,Btubulin mRNA steady state levels and internode elongation rates vary concomitantly in light-grown and etiolated soybean seedlings. Internodes of etiolated seedlings exhibited elongation rates that were four to five fold greater than those observed in control seedlings grown under a 12 h light/dark cycle. The rapidly elongating internodes of dark-grown seedlings exhibited proportionally higher steady-state levels of jtubulin mRNA. Furthermore, subsequent illumination of the dark-grown seedlings brought about a reduction in the rate of elongation and a concomitant decrease in the steady-state level of #-tubulin mRNA.Microtubules are formed by the regulated self-assembly of the heterodimeric protein tubulin from a soluble tubulin dimer pool, and cytoplasmic microtubules are in a dynamic equilibrium with this tubulin dimer pool (18). Since microtubules can form and persist only when the tubulin dimer concentration exceeds a critical value, maintenance of the tubulin dimer pool at a level above this critical concentration is essential for microtubule formation. Where it has been examined, tubulin synthesis is regulated by a mechanism that is sensitive to changes in the amount of assembled microtubules. In cultured mammalian cells, tubulin synthesis is autoregulated by a post-transcriptional mechanism that is responsive to the size of the tubulin dimer pool (5).

Changes in the Accumulation of [alpha]- and [beta]-Tubulin Isotypes during Cotton Fiber Development

“…The high leve1 of tubulin seen in 20-DPA fibers is not surprising, since it coincides with biochemical and cytological studies of tubulin and microtubule changes in developing cotton fibers (Kloth, 1989;Seagull, 1992). High levels of tubulin in 10-DPA fibers and hypocotyls are also consistent with the observations of others who have shown that tissues made up of cells undergoing rapid elongation have higher levels of tubulin protein and tubulin mRNA than tissues in which cells are not elongating (Cyr et al, 1987;Bustos et al, 1989;Han et al, 1991;Mendu and Silflow, 1993). It is interesting that tissues in which rapid cell elongation is occumng (10-DPA fibers and hypocotyls, Fig.…”

Photoregulation of β-Tubulin mRNA Abundance in Etiolated Oat and Barley Seedlings

“…White-light-induced decreases in ,B-tubulin mRNA levels in soybeans do not have a substantial effect on ,3-tubulin protein levels (1).…”

“…Downregulation of j3-tubulin mRNA abundance has also been observed after transfer of etiolated soybean seedlings to white light (1). The mRNA levels of at least 11 genes encoding unknown proteins (8,20) exposure of dark grown plants to white light.…”

Isolation and Characterization of Three Genes Negatively Regulated by Phytochrome Action in Lemna gibba

“…The results shown in Figure 6 suggest that NPR 1 genomic clone containing the coding region of NPR3 and approximately 1.8 kilobases each of 3' and 5' flanking sequences. The two HindIII fragments that hybridize to the NPR3 cDNA in the genomic Southern blot might represent two portions of a single gene, but considering that two hybridizing genomic DNA fragments also result from BamHI digestion, it is likely that there are at least two separate NPR3 genes in Lemna.…”

“…Negative regulation of gene expression by phytochrome has been demonstrated for several phytochrome genes and for an NADPH-protochlorophyllide oxidoreductase gene (4, 34, reviewed in 36), and for an asparagine synthetase gene (7). Recently, negative regulation of f-tubulin mRNA by white light or red light has also been demonstrated (1,3).…”