Water-stress-induced inhibition of α-tubulin gene expression during growth, and its implications for reproductive success in rice

A drought-suppressed cDNA (RiP-3), encoding a putative α-tubulin protein was isolated from rice panicle at pollen-mother-cell meiosis stage. Analysis of its deduced amino acid sequence showed all the typical structural motifs for plant α-tubulins. The expression of α-tubulin transcripts was observed in all the reproductive organs of rice panicle, and in 5- or 15-day old seedlings, but not in mature leaves. Expression levels were positively correlated with the regions and periods of high growth, and the transcript level declined in parallel with drought-induced reduction in growth rates in all tissues examined. Immunoblot analysis of proteins separated by SDS-PAGE with anti-α-tubulin monoclonal antibody showed that the level of protein paralleled the changes in the transcript abundance in these organs. In situ immunolocalization of the α-tubulin protein in sections of the basal part of 5-day old seedlings showed that the highest levels of the protein were associated with the fastest growing leaf whorls, and the protein level declined upon a brief episode of water stress. Given the known critical role of tubulin in cell division and elongation, the results indicate that the expression of α-tubulin gene may be part of the events that suppress panicle elongation during water deficit, which is in turn a suspected cause of male reproductive failure and yield reduction in rice.