Identification of sucker control genes
In tobacco, depending on strong shoot apical dominance, suckers grow vigorously after topping. A sucker can develop sequentially at least three times at each axil during the cultivation period. Suckers negatively affect tobacco yield and quality. Therefore, sucker control is a key process to achieve high yields and good quality in leaf tobacco production. Many genes that control axillary meristem have been reported in many plants. Furthermore, some orthologues of those genes have been isolated in tobacco. However, the function of those genes has not been well identified in tobacco. To gain sucker control genes, we first performed screening of candidate genes that might regulate sucker growth. We selected 10 genes via BLAST analysis and 24 genes via tissue-specific gene expression profiles. Then, transgenic plants with reduced expression of total 34 genes by RNAi-mediated gene silencing were evaluated for the effects of sucker growth after topping. Among the 34 candidate genes, seven genes were shown to be involved in sucker growth. Particularly, five of the seven genes were shown to be involved in the second sucker growth. RNAi-transgenic tobaccos of these five genes showed normal growth of the first sucker, but the second sucker was suppressed. These data indicate that these genes are useful to develop low sucker tobacco varieties.