Partial unidirectional translocation from 5AL to 7BS leads to dense spike in an EMS-induced wheat mutant.

Background: As the inflorescence of wheat, spike architecture largely determines grain productivity. Dissecting the genetic basis for the spike morphology of wheat can contribute to the designation of ideal spike morphology to improve grain production.

Results: The present study characterizes a dense spike1 (ds1) mutant, derived from Nongda3753, induced by EMS treatment, which exhibits a dense spike and reduced plant height. Through bulked segregant analysis sequencing (BSA-Seq) of two segregating populations, ds1 was mapped to the short arm of chromosome 7B. Further genotypic and phenotypic analyses of the residual heterozygous lines from F₃ to F₆ of Yong3002×ds1 revealed that there was a 0-135 Mb deletion in chromosome 7B associated with the dense spike phenotype. The reads count analysis of the two bulks in BSA-Seq, along with the cytological analysis of ds1, ND3753, NIL-ds1 and NIL-Y3002, confirmed that the partial unidirectional translocation of 5AL (543-713 Mb) to 7BS (0-135 Mb) exists in ds1. This translocation led to an increase in both copy number and expression of the Q gene, which is one of the reasons for the dense spike phenotype observed in ds1.

Conclusion: Partial unidirectional translocation from 5AL to 7BS was identified in the EMS-induced mutant ds1, which exhibits dense spike phenotype. This research illustrates the effect of one chromosome structure variation on wheat spike morphology, and provides new materials with several chromosome structure variations for future wheat breeding.