tapetum - specific promoters , designated a3 and a9 and capable of driving expression of 12 . 9 kda and 11 . 6 kda proteins in arabidopsis thaliana and related proteins within the family brassicaceae , have been discovered , isolated and cloned . the promoters can be used to drive male sterility dna such as that coding for a nuclease , protease or glucanase . alternatively or in addition , male sterility can be achieved by disrupting the proper expression of the a3 and / or a9 genes , for example by transcribing rna which is antisense to the rna normally transcribed from the a3 and a9 genes , or by expressing dna coding for a ribozyme specific for at least one of the a3 and a9 genes .