Chlorophyll deficiency in the maize elongated mesocotyl2 mutant is caused by a defective heme oxygenase and delaying grana stacking.
BACKGROUND
Etiolated seedlings initiate grana stacking and chlorophyll biosynthesis in parallel with the first exposure to light, during which phytochromes play an important role. Functional phytochromes are biosynthesized separately for two components. One phytochrome is biosynthesized for apoprotein and the other is biosynthesized for the chromophore that includes heme oxygenase (HO).


RESULTS
We isolated a ho1 homolog by map-based cloning of a maize elongated mesocotyl2 (elm2) mutant. cDNA sequencing of the ho1 homolog in elm2 revealed a 31 bp deletion. De-etiolation responses to red and far-red light were disrupted in elm2 seedlings, with a pronounced elongation of the mesocotyl. The endogenous HO activity in the elm2 mutant decreased remarkably. Transgenic complementation further confirmed the dysfunction in the maize ho1 gene. Moreover, non-appressed thylakoids were specifically stacked at the seedling stage in the elm2 mutant.


CONCLUSIONS
The 31 bp deletion in the ho1 gene resulted in a decrease in endogenous HO activity and disrupted the de-etiolation responses to red and far-red light. The specific stacking of non-appressed thylakoids suggested that the chlorophyll biosynthesis regulated by HO1 is achieved by coordinating the heme level with the regulation of grana stacking.
National Maize Improvement Center of China, Key Laboratory of Crop Genetic Improvement and Genome of Ministry of Agriculture, China Agricultural University, Beijing, China ; National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
Dianyi
D
Shi
Xu
X
Zheng
Liang
L
Li
Wanhuang
W
Lin
Wenjun
W
Xie
Jianping
J
Yang
Shaojiang
S
Chen
Weiwei
W
Jin
D001483:Base Sequence; D002734:Chlorophyll / Q000172:deficiency / Q000235:genetics*; D064527:Etiolation; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D006419:Heme Oxygenase (Decyclizing) / Q000235:genetics* / Q000378:metabolism; D018546:Hypocotyl / Q000378:metabolism / Q000648:ultrastructure; D008027:Light; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010834:Phytochrome / Q000096:biosynthesis / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D020524:Thylakoids / Q000378:metabolism / Q000648:ultrastructure; D003313:Zea mays / Q000201:enzymology / Q000235:genetics*
D010940:Plant Proteins; D010834:Phytochrome; D002734:Chlorophyll; D006419:Heme Oxygenase (Decyclizing); D011494:Protein Kinases