Evolutionary expansion and functional diversification of oligopeptide transporter gene family in rice

Tao Liu,Tian Fan,Kuaifei Xia,Yaqin Wang,Mingyong Zhang,Xinlan Xu,Yuge Li,Jiqing Zeng

doi:10.1186/1939-8433-5-12

Abstract

BackgroundOligopeptide transporters (OPTs) play important roles in the mobilization of organic nitrogenous compounds and usually associate with tissues that show signs of rapid protein hydrolysis, such as germinating seeds and senescing leaves. This study is to investigate rice OPT genes.ResultsA total of sixteen OsOPT genes (Os for Oryza sative L.) were identified in the rice genome, which were then classified into six sections that belong to two subfamilies (the PT and YSL subfamily). The major mechanisms for evolutionary expansion of the sixteen genes during the rice genome evolution include segmental and tandem duplication. Calculation of the duplication event dates indicated that the sixteen genes originated from nine original OsOPT genes, and the duplication events could be classified into three evolutionary stages. The first evolutionary stage occurred approximately 50 million years ago (Mya) and involved the evolution of four new genes. The second evolutionary stage was approximately 20 Mya and was marked by the appearance of two new genes, and the third evolutionary stage was approximately 9 Mya when two new genes evolved. Mining of the expression database and RT-PCR analysis indicated that the expression of most duplicated OsOPT genes showed high tissue specificities. Diverse expression patterns for the sixteen genes were evaluated using both semi-quantitative RT-PCR and the MPSS data. Expression levels of some OsOPT genes were regulated by abiotic and biotic stresses suggesting the potential involvement of these gene products in rice stress adaptation. Five OsOPT gene mutants showed abnormal development and growth, the primary analysis of five OsOPT gene mutants suggested that they may be necessary for rice development.ConclusionsThese results suggested that rice-specific OsOPT genes might be potentially useful in improving rice.Electronic supplementary materialThe online version of this article (doi:10.1186/1939-8433-5-12) contains supplementary material, which is available to authorized users.

Highlights

Oligopeptide transporters (OPTs) play important roles in the mobilization of organic nitrogenous compounds and usually associate with tissues that show signs of rapid protein hydrolysis, such as germinating seeds and senescing leaves
Identification of OsOPT gene homologues in the rice genome A total of putative OsOPT proteins have been identified from the rice genome database by BLASTP searching
The predicated OsOPT proteins were analyzed for Pfam matches in the Pfam database to confirm the 16 putative OsOPT genes (Table 1) as oligopeptide transporter-like homologues and to identify their domains

Summary

Introduction

Oligopeptide transporters (OPTs) play important roles in the mobilization of organic nitrogenous compounds and usually associate with tissues that show signs of rapid protein hydrolysis, such as germinating seeds and senescing leaves. Nine orthologs of the PT subfamily were identified in Arabidopsis and were named sequentially from AtOPT1 to AtOPT9. Five (AtOPT1, 4, 5, 6, and 7) of the orthologs were found to be functional tetra- and penta-peptide transporters by yeast complementation assay (Koh et al 2002; Osawa et al 2006). Reduced AtOPT3 expression resulted in decreased accumulation of iron in seeds while high levels resulted in the accumulation of iron in other tissues, suggesting that AtOPT3 functions to maintain whole-plant iron homeostasis and iron nutrition of developing seeds (Stacey et al 2007). Several OPT genes were identified from other plants. BjGT1 from B. juncea was found to transport glutathione and has been implicated in mediating heavy-metal toxicity (Bogs et al 2003)

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Conclusion