Wheat bZIPC1 interacts with FT2 and contributes to the regulation of spikelet number per spike

Abstract

AbstractLoss-of-function mutations and natural variation in the geneFLOWERING LOCUS T2(FT2) in wheat have previously been shown to affect spikelet number per spike (SNS). However, while other FT-like wheat proteins interact with bZIP-containing transcription factors from the A-group, FT2 does not interact with any of them. In this study, we used a yeast-two-hybrid screen with FT2 as bait and identified a grass-specific bZIP-containing transcription factor from the C-group, designated here as bZIPC1. Within the C-group, we identified four clades including wheat proteins that show Y2H interactions with different sets of FT-like and CEN-like encoded proteins.bZIPC1andFT2expression partially overlap in the developing spike, including the inflorescence meristem. Combined loss-of-function mutations inbZIPC-A1andbZIPC-B1(bzipc1) in tetraploid wheat resulted in a drastic reduction in SNS with a limited effect on heading date. Analysis of natural variation in thebZIPC-B1(TraesCS5B02G444100) region revealed three major haplotypes (H1-H3), with the H1 haplotype showing significantly higher SNS, grain number per spike and grain weight per spike than both the H2 and H3 haplotypes. The favorable effect of the H1 haplotype was also supported by its increased frequency from the ancestral cultivated tetraploids to the modern durum and common wheat varieties. We developed markers for the two non-synonymous SNPs that differentiate thebZIPC-B1ballele in the H1 haplotype from the ancestralbZIPC-B1aallele present in all other haplotypes. These diagnostic markers are useful tools to accelerate the deployment of the favorablebZIPC-B1ballele in pasta and bread wheat breeding programs.Key MessageThe wheat transcription factor bZIPC1 interacts with FT2 and affects spikelet and grain number per spike. We identified a natural allele with positive effects on these two economically important traits.