Expression Of Rice NAC Transcription Factor OsNAC2 Reduced The Height Of Rice And Delayed The Flowering Time By Gibberellin Pathway

NAC transcription factor are one of the largest families of plant specific transcription factors. They were mainly reported to participate in plant development and environmental stress. In this study, we have cloned a NAC family transcription factor OsNAC2 in Japonica rice variety Nipponbare. Transgenic T3 plants that constitutively overexpressed OsNAC2 showed shorter internode, shorter spikelet and lower yield. Furthermore, the flowering date of overexpression transgenic line OX 11 had delayed five days. Microarray analyses revealed that the expression of genes, like OsKO2, which takes part in gibberellin biosynthesis were down-regulated, the expression of OsEATB which represses the expression of gibberellin biosynthesis and SLRL which acts as a repressor in gibberellin signal pathway were up-regulated. It was also found that transgenic seedlings were more insensitive to gibberellin. By measuring the content of gibberellins in OX11 and the wide type, the content of GA53, which is the product of OsKO2, was significant lower than that of the wide type. But there was no difference about the content of bioactive GA1 between OX11 and the wide type. Therefore, it was the repression of gibberellin signal not the reduction in gibberellin biosynthesis that reduced the height of rice by overexpression of OsNAC2. The expression of OsMADS50 and RFL, which take part in the flowering transition by gibberellin pathway, were not changed in OX11.OsNAC2 might repress the expression of Hd3a by some other genes that downstream of RFL to delay the flowering date.As in rice, transgenic Arabidopsis that ectopically expressed OsNAC2 had more rosette leaves, reduced seed production and delayed flowering time. The homozygous line OXN1 overexpressed OsNAC2 were more insensitive to GA3 application, and more sensitive to PAC during seed germination. And OXN1 had shorter anther filaments and produced less seed than that of the wide type Arabidopsis. The expression of RGI and RGL were higher than that of the wide type. The results showed that OsNAC2 also repressed the gibberellin signal pathway in Arabidopsis.Taken together, OsNAC2 regulated the height of rice and the flowering time by mediating the gibberellin signal pathway.