REPRESSION OF THE HIGH-METHIONINE ZEIN GENE IN THE MAIZE INBRED LINE MO17

The methionine content in maize kernels is largely determined by the level of a methionine-rich 10 kDa protein, encoded by the gene Zps10/(22). In the maize inbred BSSS53 this gene is over-expressed compared with its normal expression in inbred lines like W64A and W22. This is in part due to the trans-acting factor Zpr10/(22). However, compared with the normal level of expression, this gene is under-expressed in the inbred Mo17 and the high-methionine zein accumulates to very low levels. Therefore, differential expression of this gene between BSSS53 and Mo17 is even larger than in other inbred lines of maize. Repression of 10 kDa zein expression in Mo17 is not due to the translatability of 10 kDa zein mRNA or a cis-acting mutation in the mRNA and neither is it due to a change in the transcription rate per se. However, steady state levels of mRNA appear to be controlled in trans by narrowing the developmental time frame of mRNA accumulation.