Genetic Effect,Haplotype Variation And Selection Of TaNAC020 In Global Wheat Breeding

NAC proteins constitute one of the largest plant specific transcription factor families among wide range of plants.NAC transcription factors have been mostly reported to play important roles against stress factors.Reports,documented to identify NAC involvement in growth and development are still rare.In present study,TaNAC020 homoeologous genes located on chromosomes 7A,7B and 7D were isolated through expression analysis in developing endosperm of wheat(Triticum aestivum L.).The expression patterns of TaNAC020 s were also investigated in Chinese Spring at different growth stages.Expression pattern analysis in wheat revealed that TaNAC020 s are highly expressed in developing grains,constitutively expressing in roots,stems and leaves at low level.Overexpression of TaNAC020-B in rice results showed significantly increased grains per spike and high density starch in the grains,demonstrating positive effect of TaNAC020 in starch synthesis and accumulation.Development of mutant wheat further validated the role of TaNAC020 s in grain development and wheat yield.Mutants’ nac-7A/B resulted in dramatically reduced seed number per spike and developed shrunken and smaller seeds with decreased TKW.Further,mutants’ nac-7A/B showed delayed initiation of A-type starch synthesis and decreased number of A-type starch granules.Beside grain development and starch synthesis,we revealed mutants have negative effect on root development and root shape.The three homology copies of TaNAC020 were designated as TaNAC020-A,TaNAC020-B and TaNAC020-D according to their chromosomal location.Gene structure analysis showed that TaNAC020-A/B were consisted of two exons and one intron while TaNAC020-D endures intron less structure.Seven and eight SNPs were identified in TaNAC020-A and-B respectively,whereas,no sequence polymorphism was identified in TaNAC020-D within a high diversity panel containing 34 collections.KASP markers were developed on the selected SNP sites.Association analysis was implemented to investigate the correlations between TaNAC020-A/B haplotypes/alleles and agronomic traits.For TaNAC020-A two KASP markers formed three haplotypes i.e.HAP-A-1/2/3.Hap-A-2 was the favored haplotype for higher grain yield.Single KASP marker was developed on the selected SNP site for TaNAC020-B forming two haplotypes i.e.HAP-B-1/2.HAP-B-2 was favored for higher thousand kernel weight and higher kernel number.Haplotype association with root related traits indicated the significant role of TaNAC020-A in root dry weight at booting and mid grain filling stage.Geographic distribution and allelic frequency showed that our favored haplotypes were positively selected in Chinese,Pakistani,Russian,North American,CIMMYT and European(HAP-A-2,HAP-B-2)wheat breeding,but the HAP-A-3 was favored in rain-fed areas.This study demonstrated that TaNAC020 s have significant effect on grain development and starch synthesis and accumulation and are one of the main regulators of grain size and grain number and have potential for utilization in wheat breeding to improve grain yield in wheat.The developed molecular markers can be instrumental in marker assisted selection for genetic improvement and germplasm enhancement in wheat.