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Plant Sci. 2016 Nov;252:133-143. doi: 10.1016/j.plantsci.2016.07.012. Epub 2016 Jul 21.

GL2-type homeobox gene Roc4 in rice promotes flowering time preferentially under long days by repressing Ghd7.

Author information

1
Crop Biotech Institute, Kyung Hee University, Yongin 446-701, Republic of Korea.
2
Crop Biotech Institute, Kyung Hee University, Yongin 446-701, Republic of Korea; Department of Life Science, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea.
3
The Key Laboratory of Plant Cell Engineering and Germplasm Innovation, Ministry of Education, College of Life Science, Shandong University, Jinan 250100, People's Republic of China.
4
Crop Biotech Institute, Kyung Hee University, Yongin 446-701, Republic of Korea. Electronic address: genean@khu.ac.kr.

Abstract

Under long day (LD) lengths, flowering can be delayed in rice by modulating several regulatory genes. We found activation tagging lines that showed an early flowering phenotype preferentially under LD conditions. Expression of Rice outermost cell-specific gene 4 (Roc4), encoding a homeodomain Leu-zipper class IV family protein, was significantly increased. Transcript levels of Grain number, plant height, and heading date7 (Ghd7) were significantly reduced while those of Ghd7 downstream genes were increased. However, other flowering regulators were unaffected. Whereas constitutive overexpression of Roc4 in 'Dongjin' japonica rice, which carries active Ghd7, also caused LD-preferential early flowering, its overexpression in 'Longjing27' rice, which is defective in functional Ghd7, did not produce the same result. This confirmed that Roc4 regulates flowering time mainly through Ghd7. Phytochromes and O. sativa GIGANTEA (OsGI) function upstream of Roc4. Transgenic plants showed ubiquitous expression of the β-glucuronidase reporter gene under the Roc4 promoter. Furthermore, Roc4 had transcriptional activation activity in the N-terminal region of the StAR-related lipid-transfer domain. All of these findings are evidence that Roc4 is an LD-preferential flowering enhancer that functions downstream of phytochromes and OsGI, but upstream of Ghd7.

KEYWORDS:

Flowering; Ghd7; HD-ZIP IV; Roc4

PMID:
27717449
DOI:
10.1016/j.plantsci.2016.07.012
[Indexed for MEDLINE]

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