Osmotin Gene Expression Is Posttranscriptionally Regulated

Accumulation of both osmotin mRNA and osmotin protein in tissues of tobacco (Nicotiana tabacum L. var Wisconsin 38) is subject to complex developmental control. Osmotin was found to be most abundant in tobacco roots and in tissues of the outer stem comprised primarily of epidermis, and it was less abundant in the corolla. It was a minor protein in other tissues and was undetectable in some tissues, including those of developing and mature seeds. The mRNA abundances did not always reflect the amount of protein accumulation because in some tissues high levels of mRNA but not protein were measured and vice versa. Accumulation of osmotin mRNA but not protein occurred in some plant tissues due to treatment with abscisic acid, wounding, and tobacco mosaic virus infection. Ethylene induced the accumulation of osmotin mRNA and, to a small extent, protein in seedlings, but was ineffective with cultured cells. Exposure of cultured cells and plants to NaCl caused high levels of both mRNA and the protein to accumulate. Thus, the accumulation of osmotin mRNA is controlled developmentally and by at least five hormonal or environmental signals. However, posttranscriptional processes can limit osmotin accumulation.