Transcriptomic insights into the genetic basis of improved Fusarium crown rot resistance during wheat allohexaploidization

Background: Fusarium crown rot (FCR) is a chronic disease of cereals worldwide. Compared with tetraploid wheat, hexaploid wheat is more resistant to FCR infection, but little is known about the contributions of allohexaploidization to wheat FCR resistance. In this study, we compared FCR responses of 10 synthetic hexaploid wheats (SHWs) and their tetraploid and diploid parents and then further analyzed transcriptome data from two SHWs and their parents. Results We observed that stronger FCR resistance emerged immediately in the SHWs following allohexaploidization. The transcriptome analysis suggested that multiple defense pathways responsive to FCR infection were stronger in the SHWs than in the parents. In particular, dozens of phenylalanine ammonia lyase (PAL) genes, involved in lignin and salicylic acid (SA) biosynthesis, exhibited a higher degree of response to FCR infection in the SHWs. Physiological measurements later confirmed that PAL activities and SA and lignin contents of the stem bases of the SHWs were higher than those of the tetraploid parents. Conclusion Overall, these findings imply that the stronger FCR resistance of hexaploid wheat compared with tetraploid wheat is probably due to changes in PAL-mediated lignin and SA biosynthesis pathways after allohexaploidization.