Os04g0473900

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DWA1 encodes an enzymatic megaprotein conserved in vascular plants,and DWA1 controls drought resistance by regulating drought-induced cuticular wax deposition in rice.

Annotated Information

Function

DWA1 encodes an enzymatic megaprotein (2,391 aa in length) conserved in vascular plants, including an oxidoreductase-like domain, a prokaryotic nonribosomal peptide synthetase-like module, an AMP-binding domain, and an allene oxide synthase-like domain. The AMP-binding domain exhibits in vitro enzymatic activity in activating long-chain fatty acids to form acyl-CoA. Expression pattern analysis shows that DWA1 is preferentially expressed in vascular tissues and epidermal layers and strongly induced by drought stress. The dwa1 mutant was highly sensitive to drought stress compared to the WT and DWA1-functional complementation (DWA1-FC)plants restored drought resistance. Further dissections uncovers that the dwa1 mutant was impaired in cuticular wax accumulation and significantly suppressed many wax-related genes expression under drought conditions and reduced levels of very-long-chain fatty acids. Conversely, plants overexpressing DWA1 were significantly up-regulated many wax-related genes expression under drought conditions and elevated levels of very-long-chain fatty acids. The results suggest that DWA1 controls drought resistance by regulating drought-induced cuticular wax deposition in rice[1].

Mutation

Fig.1 Screening of mutants(from reference[1])
Fig.2 phenotypic analysis and the expression levels of wax-related rice genes in the dwa1 mutant and WT(from reference[1])

(1) Screening of mutants(Identification of the drought-hypersensitive dwa1 mutant in rice.)
dwa1 mutant is observed by inserting T-DNA in the sixth exon of DWA1(Fig.1A and B).RT-qPCR analysis of DWA1 in WT and mutant tissues(leaf and panicle) indicate that dwa1 is a loss of-function mutant because of no transcript found in the mutant(Fig.1C and D).
(2) phenotypic analysis and the expression levels of wax-related rice genes in the dwa1 mutant and WT
During the course of drought treatment, the mutant wilted and exhibited leaf rolling earlier than the WT. After severe drought treatment followed by rewatering, more than 90% of the WT plants survive, whereas the dwa1 mutant plants are almost dead(Fig.2A and C). Water loss rate of mutant is faster than WT(Fig.2B).Furthermore, SEM analysis indicate that the deposition of vertical plate-like wax crystals on the dwa1 leaf cuticle is severely reduced under normal and drought conditions in contrast to WT leaf(Fig.2D). The contents of individual FA components is obvious difference between the dwa1 mutant and WT. Among them, VLCFAs are significantly reduced, whereas the levels of are slightly higher in the dwa1 mutant(Fig.2E). The gene expression levels of wax-related genes are obviously different under drought treatment(Fig.2F)
(3) functional complementation assay analysis
DWA1-functional complementation(DWA1-FC)lines which is inserted the full-length genomic fragment of DWA1 into the dwa1 mutant restore drought resistance(Fig.3).
(4) Overexpression of DWA1 analysis
There are three independent overexpression plants(U7,U9 and U10) and a negative control (U4),and there is no visual differences in the epicuticular wax load compared with the control (Fig. 4B).But the VLCFA constituents increase in the overexpression lines compared with WT. However, the contents of LCFAs are significantly reduced in the overexpression plants. The alkanes and primary alcohols showed no significant changes (Fig. 4C). Under normal growth conditions, the expression levels of wax-related genes enhance in the overexpression plants (Fig.4D).

Expression

(1)qRCR results show that DWA1 expression level is very low and undetectable at the vegetative stages but is relatively high at the reproductive stages(Fig.5A).
(2)Using a GUS reporter gene driven by a DWA1 promoter detects that DWA1 expression is mainly in the mature organs, such as in mature leaves (Fig.5B1 and 2), axillary bud (Fig.5B3), young panicle (Fig.5B4),spikelet (Fig.5B5), stem (Fig.5B6), young panicle (Fig.5B7), pistil (Fig.5B8), stamen (Fig.5B9), young embryo (Fig.5B10), SEM picture of rice leaf cuticle (Fig.5B11), cross-sections of stem (Fig.5B12) and leaf (Fig.5B13),and semithin sections of leaf (Fig.5B14-15).In addition,SEM observation shows that the GUS staining in leaves is mainly distributed along the silica-cork cell lines in the cuticle.Cross-sections and semithin sections indicate that DWA1 is expressed mainly in vascular tissues and epidermal cell layers.
(3)What's more,after various phytohormones treatment,DWA1 expresses higher,such as abscisic acid, jasmonic acid, indole-3-acetic acid, and gibberellic acid (Fig.5C).
(4)Under drought treatment,GUS staining shows thatDWA1 is induced.For example,in Fig.6B,GUS staining in leaf before (1 and 3) and after (2 and 4) drought stress is shown.

Evolution

At present,DWA1,likely to a megaenzyme,has five domains at least. The N terminus of DWA1 is an oxidoreductase-like domain,and closely followed by the AMP-binding domain(A domain)Then,two repeats of a phosphopantetheine-binding subdomain follow the A domain and feature a thiolation domain (T domain).An allene oxide synthase (AOS)-like domain is located between the second and third repeats of the left-handed β-helix (LbH) domain at the C-terminal region[1](Fig.7).What's more,homologous sequences with DWA1are all from microorganisms.Nonribosomal peptide synthetase(NRPS),a megaenzyme needed for nonribosomal peptides synthesis in bacteria and filamentous fungi[2],is a major branch of the AMP-binding enzyme superfamily.More importantly,both these homologous sequences and DWA1 have an NRPS module, including adenylation domain, followed by a thiolation domain catalyzing the activation and thiolation reaction of an amino acid instead of a carboxyl substrate for acyl-CoA synthetase.These features suggest that DWA1 and its plant homologs may be derived from a prokaryotic NRPS rather than the acyl-CoA synthetase family, which possesses only the A domain[1].

Labs working on this gene

  • National Key Laboratory of Crop Genetic Improvement, National Center of Plant Gene Research (Wuhan), Huazhong Agricultural University, Wuhan,China

References

  1. 1.0 1.1 1.2 1.3 1.4 Xiaoyi Zhu, Lizhong Xiong.(2013)Putative megaenzyme DWA1 plays essential roles in drought resistance by regulating stress-induced wax deposition in rice.PANS 110(44): 17790-17795.
  2. Marahiel MA, Stachelhaus T, Mootz HD.(1997) Modular peptide synthetases involved in nonribosomal peptide synthesis.Chem Rev 97(7):2651–2674.

Structured Information