Three genomes differentially contribute to the biosynthesis of benzoxazinones in hexaploid wheat

Abstract

Hexaploid wheat (Triticum aestivum) accumulates benzoxazinones (Bxs) as defensive compounds. Previously, we found that five Bx biosynthetic genes, TaBx1-TaBx5, are located on each of the three genomes (A, B, and D) of hexaploid wheat. In this study, we isolated three homoeologous cDNAs of each TaBx gene to estimate the contribution of individual homoeologous TaBx genes to the biosynthesis of Bxs in hexaploid wheat. We analyzed their transcript levels by homoeolog-or genome-specific quantitative RT-PCR and the catalytic properties of their translation products by kinetic analyses using recombinant TaBX enzymes. The three homoeologs were transcribed differentially, and the ratio of the individual homoeologous transcripts to total homoeologous transcripts also varied with the tissue, i.e., shoots or roots, as well as with the developmental stage. Moreover, the translation products of the three homoeologs had different catalytic properties. Some TaBx homoeologs were efficiently transcribed, but the translation products showed only weak enzymatic activities, which inferred their weak contribution to Bx biosynthesis. Considering the transcript levels and the catalytic properties collectively, we concluded that the homoeologs on the B genome generally contributed the most to the Bx biosynthesis in hexaploid wheat, especially in shoots. In tetraploid wheat and the three diploid progenitors of hexaploid wheat, the respective transcript levels of the TaBx homoeologs were similar in ratio to those observed in hexaploid wheat. This result indicates that the genomic bias in the transcription of the TaBx genes in hexaploid wheat originated in the diploid progenitors and has been retained through the polyploidization.biosynthetic genes ͉ homoeolog ͉ polyploidization

Cloning and comparative analysis of carotenoid β-hydroxylase genes provides new insights into carotenoid metabolism in tetraploid (Triticum turgidum ssp. durum) and hexaploid (Triticum aestivum) wheat grains

“…Previous studies showed that homeologs of the same metabolic gene could also contribute differently to metabolite biosynthesis and accumulation in hexaploid wheat (Nomura et al, 2005). In several instances, significant differences in HYD1-or HYD2-specific homeolog expression among different genomes (A, B, and D genomes) were observed (Fig.…”

Genetic and Epigenetic Alteration among Three Homoeologous Genes of a Class E MADS Box Gene in Hexaploid Wheat

“…In Ha, a locus that influences grain hardness, a large genomic deletion has occurred independently in the A and B genomes, and only the Ha locus genes present on the D genome (Pina, Pinb, and Gsp-1) are functional (Chantret et al, 2005). In Ta Bx, a gene responsible for biosynthesis of benzoxazinones (Bx), expression analysis and the determination of the proteins' catalytic properties revealed that a homoeolog from the B genome is generally the largest contributor to Bx biosynthesis (Nomura et al, 2005). These studies indicated that expression of homoeologous genes is regulated by genetic or epigenetic mechanisms.…”

Signals that stop the rot: Regulation of secondary metabolite defences in cereals

“…They are especially relevant during infection by necrotrophic pathogens, which rely on tissue injury and host cell death for effective infection [7]. Benzoxazinoids (BXs) are the predominant phytoanticipin in the major Poaceae crop plants, maize and wheat, but are absent from oat, rice and sorghum [10][11][12][13]. Interestingly, unlike Poaceae crop plants, where BXs are limited to seedlings or young plants, dicot plants accumulate BXs during all developmental stages in both above and below-ground parts [14].…”

“…Instead, this crop relies heavily on phytoanticipins such as BXs for protection against infection [12]. The principal BX in maize and wheat is 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) [13] whereas dicot plants only produce the DIMBOA precursor, DIBOA, and its glucoside DIBOA-glc [6].…”

“…Homeologs of TaBx1 and TaBx2 are positioned on chromosome 4 in all three genomes, while TaBx3 to TaBx5 homeologs are situated on chromosome 5 in all three genomes. Despite the physical separation, transcription of TaBx1 to TaBx5 is synchronized, though each genome contributes disproportionately to the detected BX load [12,121].…”