Characteristics of MADS-box and SUPERMAN genes in tobacco cytoplasmic male sterile line K326

Cytoplasmic male sterility (CMS) is an important tool for hybrid production and a good system for studying the interaction between nucleus and cytoplasm, but its mechanism is still unclear. The relationship between stamen abnormality and the relative expression levels of flower development genes in tobacco CMS line K326 was studied. The CMS line K326 was derived from a natural variation in Nicotiana tabacum and was bred by continuous backcross of flue-cured tobacco variety K326. It has not only stamens with carpelloid, but also stamens with petaloid, and the base of abnormal stamens is fused into a whole. In this study, we identified MADS-box genes and SUPERMAN genes of whole genome, which controlled the flower development in N. tabacum and analyzed their chromosomal localization and collinearity. The cis-acting elements of B genes and SUPERMAN genes were predicted, and their expression characteristics in flower buds at different stages in both CMS line and its maintainer line were studied. The results showed that 160 MADS-box genes and 5 SUPERMAN genes were identified in the genome of tobacco, including 4 PI genes, 3 AP3 genes, and 7 B genes. There were 79 MADS-box genes scattered on 22 chromosomes, and 3 SUPERMAN genes distributed on 3 chromosomes. Collinearity analysis showed that tandem and fragment DNA duplication and multiplication were the driving forces of the expansion of MADS- box gene family in tobacco. The abnormal stamens of CMS line K326 appeared at small bud stage, suggesting that the abnormal stamens in CMS line K326 were the result of early meristem development defects. The qRT-PCR showed that 7 B genes and 1 SUPERMAN gene were expressed both in CMS line K326 and its maintainers. The relative expression level of PI gene NitMADS115 in the maintainer line was higher than that in CMS line at all stages. The relative expression levels of AP3 genes NitMADS72 and NitMADS100 in maintainer lines were lower than those in CMS lines. Other genes were down-regulated at small bud stage and large bud stage, and up-regulated at middle bud stage. The SUPERMAN gene could only be detected at small bud and middle bud stage of the maintainer line, but not at bud stages of CMS line. Analysis of cis-acting elements showed that NitMADS115 had an auxin response element AuxRR. The study indicates that auxin might play an important role in cytoplasmic retrograde regulation of nucleus in tobacco.