GNI-A1mediates trade-off between grain number and grain weight in tetraploid wheat

Abstract

15Grain yield is a highly polygenic trait determined by the number of grains per unit area, as well as 16 by grain weight. In wheat, grain number and grain weight are usually negatively correlated. Yet, 17 the genetic basis underlying trade-off between the two is mostly unknown. Here, we fine-mapped 18 a grain weight QTL using wild emmer introgressions in a durum wheat background, and showed 19 that grain weight is associated with the GNI-A1 gene, a regulator of floret fertility. In-depth 20 characterization of grain number and grain weight indicated that suppression of distal florets by 21 the wild emmer GNI-A1 allele increase weight of proximal grains in basal and central spikelets 22 due to alteration in assimilate distribution. Re-sequencing of GNI-A1 in tetraploid wheat 23 demonstrated the rich allelic repertoire of the wild emmer gene pool, including a rare allele which 24 was present in two gene copies and contained a non-synonymous mutation in the C-terminus of 25 the protein. Using an F2 population generated from a cross between wild emmer accessions 26 Zavitan, which carries the rare allele, and TTD140, we demonstrated that this unique 27 polymorphism is associated with grain weight, independent of grain number. Moreover, we 28 showed, for the first time, that GNI-A1 proteins are transcriptional activators and that selection in 29 domesticated wheat targeted compromised activity of the protein. Our finding expand the 30 knowledge of the genetic basis underlying trade-off between key yield components and may 31 contribute to breeding efforts for enhanced grain yield. 32 33 Recently, the quantitative trait locus Grain Number Increase 1 (GNI1) was identified and 62 characterized as a homeodomain leucine zipper class I (HD-Zip I) transcription factor. Reduced 63 function mutation (N105Y) within the conserved homeodomain of GNI-A1, and knockdown of 64 4 GNI1 in transgenic hexaploid wheat, indicated that it is a suppressor of floret fertility. Transcript 65 abundance of GNI-B1 (orthologous copy on B genome) was negligible in floral organs of tetraploid 66 and hexaploid wheat, and was suggested to be pseudogenized in the genome of ancestral Aegilops 67 species (Sakuma et al. 2019). 68 Potential GW, defined as the intrinsic capacity of the grain to accumulate dry matter 69 (Bremner and Rawson 1978), is relatively low in distal grain positions. Several studies indicated 70 that the negative relationship between average GN and GW is an outcome of the high proportion 71 of low potential GW in high yielding cultivars (Acreche and Slafer 2006; Ferrante et al. 2015; 72 Fischer 2008; Miralles and Slafer 1995). Alternatively, Brenner and Rawson (Bremner and 73 Rawson 1978) showed that distal grains have similar potential GW as proximal grains. In addition, 74 removal of florets prior to grain filling increased weight of the remaining grains (Calderini and 75 Reynolds 2000b; Fischer and HilleRisLambers 1978), suggesting a degree of growth limitation 76 imposed by competition for insufficient source. 77 The physiological...

Roadmap for Accelerated Domestication of an Emerging Perennial Grain Crop

“…Currently, the best seed set rates in T. intermedium are as low as 30% and increasing seed set would be a Trends in Plant Science rapid way to boost yield. Information concerning the genetic basis for fertility and seed set has recently become available for wheat and barley [62,63]. The GNI1 gene encodes an HD-Zip I transcription factor and its mutations in wheat and barley have led to increased floret fertility, higher grain number per spike, and higher yields [63,64].…”

“…Information concerning the genetic basis for fertility and seed set has recently become available for wheat and barley [62,63]. The GNI1 gene encodes an HD-Zip I transcription factor and its mutations in wheat and barley have led to increased floret fertility, higher grain number per spike, and higher yields [63,64]. Wheat GNI-A1 (SPT19245) has been under selection during domestication and its reduced function in domesticated wheat is the result of an Asn105Tyr mutation in the otherwise conserved HD domain.…”

Molecular Mapping and Genomics of Grain Yield in Durum Wheat: A Review

“…Final KW is the result of the interplay between potential kernel weight (sink) and the actual supply of assimilates per kernel during kernel filling (source). Therefore, GNI-A1 participates in the trade-off between kernel number and kernel weight due to alterations in the assimilate distribution [ 119 , 120 ]. In this sense, Marcotuli et al [ 121 ] identified three putative candidate genes for kernel number per spike.…”

Unlocking the relationships among population structure, plant architecture, growing season, and environmental adaptation in Henan wheat cultivars

“…A recently cloned gene, GNI, on chromosome 2A shows pleiotropic effects on KPS and TKW [44]. However, owing to the location of its homoeologues on 2B, QTL-ple2B is not the same gene [44,45]. Given the high correlation between GFR and TKW, QTL-ple2B is a novel locus that explains the genetic basis of the trade-off between TKW (GFR) and SN.…”