Grain yield is a highly polygenic trait determined by the number of grains per unit area, as well as by grain weight. In wheat, grain number and grain weight are usually negatively correlated. Yet, the genetic basis underlying trade-off between the two is mostly unknown. Here, we fine-mapped a grain weight QTL using wild emmer introgressions in a durum wheat background, and showed that grain weight is associated with the GNI-A1 gene, a regulator of floret fertility. In-depth characterization of grain number and grain weight indicated that suppression of distal florets by the wild emmer GNI-A1 allele increase weight of proximal grains in basal and central spikelets due to alteration in assimilate distribution. Re-sequencing of GNI-A1 in tetraploid wheat demonstrated the rich allelic repertoire of the wild emmer gene pool, including a rare allele which was present in two gene copies and contained a non-synonymous mutation in the C-terminus of the protein. Using an F2 population generated from a cross between wild emmer accessions Zavitan, which carries the rare allele, and TTD140, we demonstrated that this unique polymorphism is associated with grain weight, independent of grain number. Moreover, we showed, for the first time, that GNI-A1 proteins are transcriptional activators and that selection targeted compromised activity of the protein. Our finding expand the knowledge of the genetic basis underlying trade-off between key yield components and may contribute to breeding efforts for enhanced grain yield.
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...
Jojoba (Simmondsia chinensis) is a wax crop cultivated mainly in arid and semi-arid regions. This crop has been described as an alternate-bearing plant, meaning that it has a high-yield year (“on-year”) followed by a low-yield year (“off-year”). We investigated the effect of fruit load on jojoba’s vegetative and reproductive development. For two consecutive years, we experimented with two high-yielding cultivars—Benzioni and Hazerim—which had opposite fruit loads, i.e., one was under an on-year load, while the other was under an off-year load simultaneously. We found that removing the developing fruit from the shoot during an off-year promotes further vegetative growth in the same year, whereas in an on-year, this action has no effect. Moreover, after fruit removal in an on-year, there was a delay in vegetative growth renewal in the consecutive year, suggesting that the beginning of the growing period is dependent on the previous year’s yield load. We found that seed development in the 2018 season started a month earlier than in the 2017 season in both cultivars, regardless of fruit load. This early development was associated with higher wax content in the seeds. Hence, the wax accumulation rate, as a percentage of dry weight, was affected by year and not by fruit load. However, on-year seeds stopped growing earlier than off-year seeds, resulting in smaller seeds and an overall lower amount of wax per seed.
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