Target-Site Mutations and Expression of ALS Gene Copies Vary According to Echinochloa Species.

Silvia Panozzo,Elisa Mascanzoni,Giliardi Dalazen,Laura Scarabel,Maurizio Sattin,Andrea Milani,Patrick J Tranel,Aldo J Merotto

doi:10.3390/genes12111841

Abstract

The sustainability of rice cropping systems is jeopardized by the large number and variety of populations of polyploid Echinochloa spp. resistant to ALS inhibitors. Better knowledge of the Echinochloa species present in Italian rice fields and the study of ALS genes involved in target-site resistance could significantly contribute to a better understanding of resistance evolution and management. Using a CAPS-rbcL molecular marker, two species, E. crus-galli (L.) P. Beauv. and E. oryzicola (Vasinger) Vasing., were identified as the most common species in rice in Italy. Mutations involved in ALS inhibitor resistance in the different species were identified and associated with the ALS homoeologs. The relative expression of the ALS gene copies was evaluated. Molecular characterization led to the identification of three ALS genes in E. crus-galli and two in E. oryzicola. The two species also carried different point mutations conferring resistance: Ala122Asn in E. crus-galli and Trp574Leu in E. oryzicola. Mutations were carried in the same gene copy (ALS1), which was significantly more expressed than the other copies (ALS2 and ALS3) in both species. These results explain the high resistance level of these populations and why mutations in the other ALS copies are not involved in herbicide resistance.

Highlights

IntroductionThe genus Echinochloa includes about approximately 50 annual summer species, widespread in both tropical and temperate regions and in dry (e.g., maize and soybean) or water flooded soils (e.g., rice) [1]
The genus Echinochloa includes about approximately 50 annual summer species, widespread in both tropical and temperate regions and in dry or water flooded soils [1]
Several classification keys have been proposed in the last century, but none of them have been able to adequately fulfill the task; Echinochloa species are often very difficult to distinguish due to wide intraspecific morphological and phenological variability [2]

Summary

Introduction

The genus Echinochloa includes about approximately 50 annual summer species, widespread in both tropical and temperate regions and in dry (e.g., maize and soybean) or water flooded soils (e.g., rice) [1]. A rough first classification can be done on the basis of macro-phenological differences, dividing Echinochloa species in two groups: the “red” (i.e., E. crus-galli (L.) P. E. oryzicola is the dominant and most persistent due to its complex survival strategy in flooded rice [3]. The species of both groups are annual with a C4 photosynthetic pathway [3,4] and show a great competitive advantage when they grow together with C3 crops

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