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Open Access Research article

The I2 resistance gene homologues in Solanum have complex evolutionary patterns and are targeted by miRNAs

Chunhua Wei, Hanhui Kuang, Feng Li and Jiongjiong Chen*

Author Affiliations

Key Laboratory of Horticulture Biology, Ministry of Education, and Department of Vegetable Crops, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan 430070, People’s Republic of China

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BMC Genomics 2014, 15:743  doi:10.1186/1471-2164-15-743

Published: 30 August 2014

Abstract

Background

Several resistance traits, including the I2 resistance against tomato fusarium wilt, were mapped to the long arm of chromosome 11 of Solanum. However, the structure and evolution of this locus remain poorly understood.

Results

Comparative analysis showed that the structure and evolutionary patterns of the I2 locus vary considerably between potato and tomato. The I2 homologues from different Solanaceae species usually do not have orthologous relationship, due to duplication, deletion and frequent sequence exchanges. At least 154 sequence exchanges were detected among 76 tomato I2 homologues, but sequence exchanges between I2 homologues in potato is less frequent. Previous study showed that I2 homologues in potato were targeted by miR482. However, our data showed that I2 homologues in tomato were targeted by miR6024 rather than miR482. Furthermore, miR6024 triggers phasiRNAs from I2 homologues in tomato. Sequence analysis showed that miR6024 was originated after the divergence of Solanaceae. We hypothesized that miR6024 and miR482 might have facilitated the expansion of the I2 family in Solanaceae species, since they can minimize their potential toxic effects by down-regulating their expression.

Conclusions

The I2 locus represents a most divergent resistance gene cluster in Solanum. Its high divergence was partly due to frequent sequence exchanges between homologues. We propose that the successful expansion of I2 homologues in Solanum was at least partially attributed to miRNA mediated regulation.

Keywords:
I2 locus; Ty-2; Solanaceae; Evolution; Sequence exchange; miRNA