Plant Mol Biol (2017) 93:579–592
Heme oxygenase 1 defects lead to reduced chlorophyll in Brassica
· Zonghui Yang
· Xinhua Zeng
· Jie Gao
· Jie Liu
· Bin Yi
· Jinxiong Shen
· Jinxing Tu
· Tingdong Fu
· Jing Wen
Received: 27 May 2016 / Accepted: 9 January 2017 / Published online: 20 January 2017
© Springer Science+Business Media Dordrecht 2017
impaired tetrapyrrole metabolism, especially chlorophyll
biosynthesis. According, the levels of chlorophyll inter-
mediates 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.
Keywords Brassica napus · Yellow-green leaf ·
Heme oxygenase 1 · LncRNA insertion · Tetrapyrrole
metabolism · Chlorophyll biosynthesis
Tetrapyrroles play essential roles in various biological pro-
cesses, including photosynthesis and respiration. In higher
plants, there are four classes of tetrapyrroles: chlorophyll,
heme, siroheme, and phytochromobilin (PΦB), which are
derived from a common biosynthetic pathway. Phytochro-
mobilin diﬀers from the other three tetrapyrroles because
it is a linear tetrapyrrole, whereas the others have a closed
macrocycle. Phytochromes (phys) utilize covalently bound
phytochromobilin chromophores, which can mediate pho-
toconversion between red-absorbing and far-red-absorbing
forms. Phys inﬂuence seed germination, chloroplast devel-
opment, leaf growth, pigmentation, circadian rhythms,
ﬂowering time and senescence (Franklin and Quail 2010;
Rockwell et al. 2006).
The biosynthetic pathways for phytochromobilin and
chlorophyll share precursors from 5-aminolevulinic acid
(ALA) to protoporphyrin IX (Proto IX). Proto IX is located
at the branch point of heme and chlorophyll biosynthesis.
At this point, ferrochelatase inserts Fe
into Proto IX to
form protoheme (heme b), whereas magnesium chelatase
Abstract We previously described a Brassica napus
chlorophyll-deﬁcient mutant (ygl) with yellow-green seed-
ling 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
Electronic supplementary material The online version of this
article (doi:10.1007/s11103-017-0583-y) contains supplementary
material, which is available to authorized users.
* Jing Wen
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
Key Laboratory of Biology and Genetic Improvement of Oil
Crops Oil Crops Research the Chinese Institute of Academy
of Agricultural Sciences,, Ministry of Agriculture,
Wuhan 430062, China