A robust SNP-haplotype assay for Bct gene region conferring resistance to beet curly top virus in common bean (Phaseolus vulgaris L.)

Mapping of flumioxazin tolerance in a snap bean diversity panel leads to the discovery of a master genomic region controlling multiple stress resistance genes

Introduction

Effective weed management tools are crucial for maintaining the profitable production of snap bean (Phaseolus vulgaris L.). Preemergence herbicides help the crop to gain a size advantage over the weeds, but the few preemergence herbicides registered in snap bean have poor waterhemp (Amaranthus tuberculatus) control, a major pest in snap bean production. Waterhemp and other difficult-to-control weeds can be managed by flumioxazin, an herbicide that inhibits protoporphyrinogen oxidase (PPO). However, there is limited knowledge about crop tolerance to this herbicide. We aimed to quantify the degree of snap bean tolerance to flumioxazin and explore the underlying mechanisms.

Methods

We investigated the genetic basis of herbicide tolerance using genome-wide association mapping approach utilizing field-collected data from a snap bean diversity panel, combined with gene expression data of cultivars with contrasting response. The response to a preemergence application of flumioxazin was measured by assessing plant population density and shoot biomass variables.

Results

Snap bean tolerance to flumioxazin is associated with a single genomic location in chromosome 02. Tolerance is influenced by several factors, including those that are indirectly affected by seed size/weight and those that directly impact the herbicide's metabolism and protect the cell from reactive oxygen species-induced damage. Transcriptional profiling and co-expression network analysis identified biological pathways likely involved in flumioxazin tolerance, including oxidoreductase processes and programmed cell death. Transcriptional regulation of genes involved in those processes is possibly orchestrated by a transcription factor located in the region identified in the GWAS analysis. Several entries belonging to the Romano class, including Bush Romano 350, Roma II, and Romano Purpiat presented high levels of tolerance in this study. The alleles identified in the diversity panel that condition snap bean tolerance to flumioxazin shed light on a novel mechanism of herbicide tolerance and can be used in crop improvement.

The alleles bc-ud and bc-ur (previously bc-4 gene), representing coding mutations within Vps4 AAA+ ATPase ESCRT protein, interact with other genes to condition resistance to BCMV and BCMNV in common bean

Bean common mosaic virus (BCMV) and bean common mosaic necrosis virus (BCMNV) have a damaging impact on global common bean (Phaseolus vulgaris L.) cultivation, causing potential yield losses of over 80%. The primary strategy for controlling these viruses is through host plant resistance. This research aimed to identify and validate structural variations for the bc-ud gene as revealed by long-read sequencing, develop an efficient DNA marker to assist selection of bc-ud in snap and dry beans, and examine the interactions between the bc-ud allele and other BCMV resistance genes. A gene (Phvul.005G125100) model on chromosome Pv05, encoding a vacuolar protein-sorting 4 (Vps4) AAA+ ATPase endosomal sorting complexes required for transport (ESCRT) protein, was identified as the best candidate gene for bc-ud. An 84-bp repetitive insertion variant within the gene, exhibited 100% co-segregation with the bc-ud resistance allele across 264 common bean accessions. The 84-bp repetitive insertion was labeled with an indel marker IND_05_36225873 which was useful for tracking the bc-ud allele across diverse germplasm. A different single nucleotide polymorphism variant within the same candidate gene was associated with the bc-4 gene. Segregation in F2 populations confirmed bc-ud and bc-4 were alleles, so bc-4 was renamed bc-ur to fit gene nomenclature guidelines. The interactions of bc-ud and bc-ur with other resistance genes, such as bc-1 (receptor-like kinase on Pv03) and bc-2 (Vps4 AAA+ ATPase ESCRT protein on Pv11), validated gene combinations in the differential "host groups" effective against specific BCMV/BCMNV "pathogroups." These findings increase our understanding of the Bc-u locus, and enhance our ability to develop more resilient bean varieties through marker-assisted selection, reducing the impact of BCMV and BCMNV.