S. Giani et D. Breviario, RICE BETA-TUBULINS MESSENGER-RNA LEVELS ARE MODULATED DURING FLOWER DEVELOPMENT AND IN RESPONSE TO EXTERNAL STIMULI, PLANT SCI, 116(2), 1996, pp. 147-157
Rice beta-tubulin cDNA clones have been recently isolated by different
laboratories (Kang et al. (1994) Plant Mel. Biol. 26, 1975-1979; Brev
iario et al. (1995) Plant Physiol. 108, 823-824; Koga-Ban et al. (1995
) DNA Res. 2, 21-26). Analysis of their deduced amino acid sequences s
hows the conservation of all those structural motifs typical of plant
beta-tubulins. Putative sequences for autoregulation and tubulin mRNA
stability, for GTP binding and exchange as well as for herbicides and
Ca2+ binding are present. With the use of a generic or isotype specifi
c beta-tubulin (OS-TUB16) probe we assayed the level of transcriptiona
l accumulation in different rice tissues, during flower development, c
ell elongation and in response to anoxia. We found enhanced levels of
total or isotype-16 specific beta-tubulin mRNA at early stages of flow
er development in spikelets at 8-10 days before anthesis. The lowest l
evels were observed in adult leaves. Total beta-tubulin as well as iso
type-16 specific transcript levels were strongly decreased (10-fold) i
n rice coleoptiles treated with 50 mu M abscisic acid (ABA); a more mo
dest decrease (2-fold) in the total level of rice alpha-tubulin mRNA w
as instead observed in these samples. We also show a strict correlatio
n between growth under anoxia and beta-tubulin transcriptional abundan
ce. Rice roots, unable to grow in anoxia, showed very low amount of to
tal beta-tubulin mRNA whereas rice coleoptiles, capable of elongating
under anaerobiosis, maintained high levels of total beta-tubulin trans
cripts. However, with the use of a 3' non-coding probe specific for be
ta-tubulin isotype-16, we found that the amount of this transcript is
always decreased by anoxia regardless the type of tissue analyzed.