Identification and characterization of a natural polymorphism in FT-A2 associated with increased number of grains per spike in wheat

Abstract

Key message We discovered a natural FT-A2 allele that increases grain number per spike in both pasta and bread wheat with limited effect on heading time. Abstract Increases in wheat grain yield are necessary to meet future global food demands. A previous study showed that loss-of-function mutations in FLOWERING LOCUS T2 (FT2) increase spikelet number per spike (SNS), an important grain yield component. However, these mutations were also associated with reduced fertility, offsetting the beneficial effect of the increases in SNS on grain number. Here, we report a natural mutation resulting in an aspartic acid to alanine change at position 10 (D10A) associated with significant increases in SNS and no negative effects on fertility. Using a high-density genetic map, we delimited the SNS candidate region to a 5.2-Mb region on chromosome 3AS including 28 genes. Among them, only FT-A2 showed a non-synonymous polymorphism (D10A) present in two different populations segregating for the SNS QTL on chromosome arm 3AS. These results, together with the known effect of the ft-A2 mutations on SNS, suggest that variation in FT-A2 is the most likely cause of the observed differences in SNS. We validated the positive effects of the A10 allele on SNS, grain number, and grain yield per spike in near-isogenic tetraploid wheat lines and in an hexaploid winter wheat population. The A10 allele is present at very low frequency in durum wheat and at much higher frequency in hexaploid wheat, particularly in winter and fall-planted spring varieties. These results suggest that the FT-A2 A10 allele may be particularly useful for improving grain yield in durum wheat and fall-planted common wheat varieties.

WAPO-A1 is the causal gene of the 7AL QTL for spikelet number per spike in wheat

“…A similar result has been recently reported for the FT-A2 gene, where the derived A10 allele associated with increases in SNS was found at high frequency in common wheat (~60%) but was almost absent in modern durum wheat commercial varieties (0.7%) [36]. These results suggest that other genes involved in the regulation of spike development may have differential frequencies between common and durum wheat as a result of this putative selection for large grains.…”

“…The WAPO-A1 H2 haplotype was found in only one accession from Syria in a survey of 364 durum wheat varieties [ 10 ]. Similarly, the FT-A2 A10 allele was found only in three accessions from Oman and Turkey in a survey of 417 durum wheat varieties [ 36 ]. In this study, we show that the transfer of the WAPO-A1 H2 haplotype from common wheat into the tetraploid wheat Kronos was associated with significant increases in SNS and GNS.…”

Overexpression of the WAPO-A1 gene increases the number of spikelets per spike in bread wheat

“…As previously proposed 24 , our results imply that WAPO-A1b promotes an increase in sink capacity which may require introgression into high-biomass productive varieties and cultivation under conditions that support high yield potential. The observed trade-offs are not unique to WAPO1 and have been shown in other genes that increase sink capacity such as FT2 59 and FUL2 3 . In rice it has also been reported that Os APO1 increases yield 13 , but that the effect on yield is source dependent 60 and dependent on gene expression levels as described above.…”

Overexpression of the WAPO-A1 gene increases the number of spikelets per spike in bread wheat

“…As previously proposed 24 , our results imply that WAPO-A1b promotes an increase in sink capacity which may require introgression into high-biomass productive varieties and cultivation under conditions that support high yield potential. The observed trade-offs are not unique to WAPO1 and have been shown in other genes that increase sink capacity such as FT2 51 and FUL2 3 . In rice it has also been reported that Os APO1 increases yield 13 , but that the effect on yield is source dependent 52 and dependent on gene expression levels as described above.…”