OsIAGT1 Is a Glucosyltransferase Gene Involved in the Glucose Conjugation of Auxins in Rice

Qian Liu,Ting-Ting Chen,Ji-Shan Lin,Shu-Man Zhao,Yan-Jie Li,Ting Wang,Bing-Kai Hou,Dong-Wang Xiao

doi:10.1186/s12284-019-0357-z

Qian Liu, Ting-Ting Chen + Show 6 more

Open Access

https://doi.org/10.1186/s12284-019-0357-z

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Abstract

BackgroundIn cereal crop rice, auxin is known as an important class of plant hormone that regulates a plethora of plant growth and development. Glycosylation of auxin is known to be one of the important mechanisms mediating auxin homeostasis. However, the relevant auxin glucosyltransferase (GT) in rice still remains largely unknown.ResultsIn this study, using known auxin glucosyltransferases from other species as queries, twelve putative auxin UDP-glycosyltransferase (UGT) genes were cloned from rice and the one showing highest sequence similarity, named as OsIAGT1, was expressed as recombinant protein. In vitro enzymatic analysis showed that recombinant OsIAGT1 was capable of catalyzing glucosylation of IAA, IBA and other auxin analogs, and that OsIAGT1 is quite tolerant to a broad range of reaction conditions with peak activity at 30 °С and pH 8.0. OsIAGT1 showed favorite activity towards native auxins over artificially synthesized ones. Further study indicated that expression of OsIAGT1 can be upregulated by auxin in rice, and with OsIAGT1 overexpressing lines we confirmed that OsIAGT1 is indeed able to glucosylate IAA in vivo. Consistently, ectopic expression of OsIAGT1 leads to declined endogenous IAA content, as well as upregulated auxin synthesis genes and reduced expression of auxin-responsive genes, which likely leads to the reduced plant stature and root length in OsIAGT1 overexpression lines.ConclusionOur result indicated that OsIAGT1 plays an important role in mediating auxin homeostasis by catalyzing auxin glucosylation, and by which OsIAGT1 regulates growth and development in rice.

Highlights

In cereal crop rice, auxin is known as an important class of plant hormone that regulates a plethora of plant growth and development
We found that expression of OsIAGT1 is auxin-induced, and ectopic expression of OsIAGT1 leads to declined endogenous indole-3-acetic acid (IAA) content, as well as reduced expression of auxin-responsive genes, which caused the reduced plant height and root length in OsIAGT1 overexpression lines
Identification of Putative Auxin Glycosyltransferases in Rice BLAST searches were performed in open-access rice genome databases using amino acid sequences of maize auxin UGT protein iaglu (Szerszen et al 1994) and Arabidopsis UGT84B1, UGT84B2, UGT74E2 and UGT74D1 as queries

Summary

Results

Identification of Putative Auxin Glycosyltransferases in Rice BLAST searches were performed in open-access rice genome databases using amino acid sequences of maize auxin UGT protein iaglu (Szerszen et al 1994) and Arabidopsis UGT84B1, UGT84B2, UGT74E2 and UGT74D1 as queries. Consistent with the reduced auxin content, those genes in auxin signaling pathway including the transcription repressor OsIAA1 and OsIAA14 (Tiwari et al 2001; Jain et al 2006), auxin-responsive OsARF12 (Li et al 2016) and auxin downstream gene GH3–2 (Zhang et al 2015) showed reduced expression in OE-6 and OE-7 rice plants (Fig. 7c) These results further confirmed that by glucosylation of auxin, OsIAGT1 plays an important role in regulating auxin content and activity. Combined with the results that OsIAGT1 overexpression seedlings showed higher shoots and longer roots than WT under treatment with high concentration IAA (10 or 100 uM), our data suggest that OsIAGT1 is involved in regulating auxin level and auxin response by glucosylation, which might play an important role in mediating rice growth and development

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Background

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Materials and Methods