MIT1, encoding a 15-cis-ζ-carotene isomerase (Z-ISO), regulates tiller number and stature in rice
作者： Lihua Liu#, Mengmeng Ren#, Peng Peng#, Yan Chun, Lu Li, Jinfeng Zhao, JingjingFang, Lixiang Peng, Jijun Yan, Jinfang Chu, Yiqin Wang, Shoujiang Yuan, Xueyong Li*
期刊名稱：Journal of Genetics and Genomics
文章摘要：In this study, we characterized a rice mit1 mutant that produces moderately increased tiller number with mildly reduced stature. Map-based cloning revealed that MIT1 encodes 15-cis-ζ-carotene isomerase (Z-ISO) in the carotenoid biosynthesis pathway, which is located in the chloroplasts and expressed in most tissues. Dark-grown mit1 plants accumulated higher levels of 9,15,9′-tri-cis-ζ-carotene, the substrate of Z-ISO, due to its inability to convert into 9,9'-di-cis-ζ-carotene. Even in tissues of the light-grown mit1 mutant, the contents of several carotenoids were also reduced. This finding suggests that MIT1 deficiency leads to reduced carotenoid biosynthesis. Levels of 2'-epi-5-deoxystrigol, a native SL in rice, were significantly lower in root exudates of mit1 seedlings than in wild type. The enhanced tiller bud outgrowth and mesocotyl elongation of mit1 were inhibited by application of the synthetic SL analog GR24. Because Z-ISO is an important enzyme in the carotenoid biosynthesis pathway, which is the substrate for SL biosynthesis, we assume that the increased tiller phenotype is caused by the SL deficiency. Double mutant analysis with known SL mutants d3 and d17 indicated that MIT1 controls tiller number through the SL pathway and that MIT1 is located upstream of the SL biosynthesis and signaling pathways. The roles of Z-ISO in carotenoid biosynthesis have been well characterized using the maize y9 and Arabidopsis zic1 mutants. However, the possible effect of Z-ISO on plant processes downstream of the carotenoid biosynthesis pathway, such as the biosynthesis of SL, a caroteniod-derived plant hormone, remains poorly understood. Thus, the results of the present rice mit1 mutant study establish a direct link between carotenoid deficiency and SL-mediated shoot branching.