Zm PBF and Zm GAMYB transcription factors independently transactivate the promoter of the maize ( Zea mays ) β‐carotene hydroxylase 2 gene

• Published in: The New phytologist Vol. 222; no. 2; pp. 793 - 804
• Main Authors: Jin, Xin, Bai, Chao, Bassie, Ludovic, Nogareda, Carmina, Romagosa, Ignacio, Twyman, Richard M., Christou, Paul, Zhu, Changfu
• Format: Journal Article
• Language: English
• Published: 01-04-2019
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.15614

The maize (
Zea mays
) enzyme β‐carotene hydroxylase 2 (Zm
BCH
2) controls key steps in the conversion of β‐carotene to zeaxanthin in the endosperm. The
Zm
BCH
2
gene has an endosperm‐preferred and developmentally regulated expression profile, but the detailed regulatory mechanism is unknown.
To gain insight into the regulation of
Zm
BCH
2
, we isolated 2036 bp of the 5′‐flanking region containing the 263 bp 5′‐untranslated region (5′‐
UTR
) including the first intron. We linked this to the β‐glucuronidase reporter gene
gusA
.
We found that high‐level expression of
gusA
in rice seeds requires the 5′‐
UTR
for enhanced activation. Truncated variants of the
Zm
BCH
2
promoter retained their seed‐preferred expression profile as long as a prolamin box and
AACA
motif were present.
We identified candidate genes encoding the corresponding transcription factors (Zm
PBF
and Zm
GAMYB
) and confirmed that their spatiotemporal expression profiles are similar to
Zm
BCH
2
. Both Zm
PBF
and Zm
GAMYB
can transactivate
Zm
BCH
2
expression in maize endosperm. To eliminate potential confounding effects in maize, we characterized the regulation of the minimal promoter region of
Zm
BCH
2
in transgenic rice. This revealed that Zm
PBF
and Zm
GAMYB
independently transactivate the
Zm
BCH
2
promoter. The mechanism that underpins our data provides an exciting new strategy for the control of target gene expression in engineered plants.