Heterologous expression of rice 9-cis-epoxycarotenoid dioxygenase 4 (OsNCED4) in Arabidopsis confers sugar oversensitivity and drought tolerance
Hwang et al. Bot Stud
Heterologous expression of rice 9-cis-epoxycarotenoid dioxygenase 4 (OsNCED4) in Arabidopsis confers sugar oversensitivity and drought tolerance
San‑Gwang Hwang 0
ChiaY‑un Lee 2
Ching‑Shan Tseng 1
0 Department of Horticulture, National Chung Hsing University , 145 Xingda Road, South District, Taichung 40227, Taiwan, ROC
1 Taiwan Agricultural Research Institute, Council of Agriculture , Executive Yuan, No.189, Zhongzheng Road, Wufeng District, Taichung 41362, Taiwan, ROC
2 Institute of Plant and Microbial Biology, Academia Sinica , Taipei 11529, Taiwan, ROC
Background: The 9‑ cis‑ epoxycarotenoid dioxygenases OsNCED4 was cloned from rice in conjunction with OsNCED 1‑ 3 and 5, of which 3 has been shown to function in ABA biosynthesis and alteration of leaf morphology. In higher plants, NCEDs have been shown to be key enzymes controlling ABA biosynthesis and belong to a differentially expressed gene family. Aside from OsNCED3, it remains largely unknown if other OsNCED genes are involved in ABA biosynthesis in rice. Thus, transgenic Arabidopsis plants overexpressing OsNCED4 were generated in the 129B08/nced3 mutant background to explore OsNCED4 function in ABA biosynthesis. Results: Heterologous expression of OsNCED4 in Arabidopsis increased ABA levels and altered plant size and leaf shape, delayed seed germination, caused sugar oversensitivity in post‑ germination growth, and enhanced tolerance to drought. The native OsNCED3 and OsNCED4 promoters were expressed in an overlapping pattern in rice seeds and young seedlings, suggesting possible functional redundancy between OsNCED3 and OsNCED4. At the one‑ leaf stage, similar regulation of OsNCED3 and OsNCED4 gene expression in roots or leaves in response to moderate salt stress (150 mM NaCl) was observed. Conclusion: Like OsNCED3, OsNCED4 is functionally active in ABA biosynthesis in rice. OsNCED3 and OsNCED4 might play redundant roles in controlling ABA biosynthesis in rice, as suggested by GUS staining assay, but this should be further analyzed through complementation of rice NCED knockout mutants.
Abscisic acid; 9‑ cis‑ epoxycarotenoid dioxygenase; Seed germination; Post‑ germination growth arrest; Drought tolerance
Background
The functions of abscisic acid (ABA) in regulation of seed
dormancy, seedling growth and development, stomatal
closure, and stress tolerance is well studied
(Jiang and Yu
2009; Zhu et al. 2009, 2011; Waterland et al. 2010; Gao
et al. 2011; Bauer et al. 2013; Merilo et al. 2015)
.
Connections among ABA, molecular signaling components, and
nutrition have been identified. For example,
Jiang and Yu
(2009)
suggested that the transcription factor AtWRKY2
regulates seed germination and post-germination
developmental arrest in Arabidopsis via its response to ABA.
At the same year, Zhu et al. (2009) reported that the
glucose-induced germination delay in rice seeds is due to the
prevention of ABA degradation, rather than an increase
in ABA biosynthesis. Zhu et al. (2011) further elaborated
that downregulation of CYP707A2 expression, a gene
encoding an ABA 8′-hydroxylase involved in ABA
catabolism, and the subsequent reduction in ABA degradation,
are closely associated with the delay of seed
germination and seedling growth in Arabidopsis. More recently,
Gao et al. (2011) characterized the protein function of
AtCPR5 and revealed that seed germination and early
seedling growth are independently regulated through the
ABA and lipoxygenase (LOX) pathways.
ABA regulates numerous physiological responses in
addition to seed germination and seedling growth.
Previous reports have shown that ABA synthesis in guard cells
is essential and sufficient for stomatal closure in response
to declined relative humidity
(Bauer et al. 2013; Merilo
et al. 2015)
. Waterland et al. (2010) demonstrated the
involvement of ABA in drought tolerance. The roles of
ABA and ABA signaling in plant abiotic stress responses,
including drought tolerance, have been recently reviewed
and discussed
(Sah et al. 2016; Vishwakarma et al. 2017)
.
In higher plants, 9-cis-epoxycarotenoid dioxygenases
(NCEDs) are thought to be the key enzymes
controlling ABA biosynthesis and stress tolerance
(Iuchi et al.
2001; Sun et al. 2012; Vishwakarma et al. 2017)
. To date,
five rice NCED genes have been reported
(Oliver et al.
2007; Welsch et al. 2008; Zhu et al. 2009)
. However,
only OsNCED3 (GenBank Accession No. AY838899)
was characterized as functionally active in ABA
biosynthesis
(Hwang et al. 2010)
. The biological functions of
the other four rice NCED genes, OsNCED1 (GenBank
Accession No. AY838897), OsNCED2 (GenBank
Accession No. AY838898), OsNCED4 (GenBank Accession
No. AY838900) and OsNCED5 (GenBank Accession
No. AY838901) have yet to be deciphered. It remains
unknown whether rice OsNCED4 gene is involved
in ABA biosynthesis or ABA-regulated physiological
processes.
Previous studies of the NCED gene family in
Arabidopsis revealed that diffe (...truncated)