Zhu Lixia, Yang Zonghui, Zeng Xinhua, Gao Jie, Liu Jie, Yi Bin, Ma Chaozhi, Shen Jinxiong, Tu Jinxing, Fu Tingdong, Wen Jing
National Key Laboratory of Crop Genetic Improvement, National Sub-center of Rapeseed Improvement in Wuhan, Huazhong Agricultural University, Wuhan, 430070, China.
Shandong Key Laboratory of Greenhouse Vegetable Biology, Shandong Branch of National Vegetable Improvement Center, Institute of Vegetables and Flowers, Shandong Academy of Agricultural Sciences, Jinan, 250100, China.
Plant Mol Biol. 2017 Apr;93(6):579-592. doi: 10.1007/s11103-017-0583-y. Epub 2017 Jan 20.
We previously described a Brassica napus chlorophyll-deficient mutant (ygl) with yellow-green seedling leaves and mapped the related gene, BnaC.YGL, to a 0.35 cM region. However, the molecular mechanisms involved in this chlorophyll defect are still unknown. In this study, the BnaC07.HO1 gene (equivalent to BnaC.YGL) was isolated by the candidate gene approach, and its function was confirmed by genetic complementation. Comparative sequencing analysis suggested that BnaC07.HO1 was lost in the mutant, while a long noncoding-RNA was inserted into the promoter of the homologous gene BnaA07.HO1. This insert was widely present in B. napus cultivars and down-regulated BnaA07.HO1 expression. BnaC07.HO1 was highly expressed in the seedling leaves and encoded heme oxygenase 1, which was localized in the chloroplast. Biochemical analysis showed that BnaC07.HO1 can catalyze heme conversion to form biliverdin IXα. RNA-seq analysis revealed that the loss of BnaC07.HO1 impaired tetrapyrrole metabolism, especially chlorophyll biosynthesis. According, the levels of chlorophyll intermediates were reduced in the ygl mutant. In addition, gene expression in multiple pathways was affected in ygl. These findings provide molecular evidences for the basis of the yellow-green leaf phenotype and further insights into the crucial role of HO1 in B. napus.
我们之前描述了一个甘蓝型油菜叶绿素缺乏突变体（ygl），其幼苗叶片为黄绿色，并将相关基因BnaC.YGL定位到一个0.35 cM的区域。然而，这种叶绿素缺陷所涉及的分子机制仍然未知。在本研究中，通过候选基因法分离出了BnaC07.HO1基因（等同于BnaC.YGL），并通过遗传互补证实了其功能。比较测序分析表明，BnaC07.HO1在突变体中缺失，而一个长链非编码RNA插入到同源基因BnaA07.HO1的启动子中。这种插入在甘蓝型油菜品种中广泛存在，并下调了BnaA07.HO1的表达。BnaC07.HO1在幼苗叶片中高度表达，编码血红素加氧酶1，该酶定位于叶绿体中。生化分析表明，BnaC07.HO1可以催化血红素转化形成胆绿素IXα。RNA测序分析显示，BnaC07.HO1的缺失损害了四吡咯代谢，尤其是叶绿素生物合成。因此，ygl突变体中叶绿素中间体的水平降低。此外，ygl中多个途径的基因表达受到影响。这些发现为黄绿叶片表型的基础提供了分子证据，并进一步深入了解了HO1在甘蓝型油菜中的关键作用。
