Vicentin, L. | bioRxiv Science

bioRxiv2025

TaExpA6, VRT-A2 and TaGW2 genes differentially affect grain weight, grain number and yield of wheat through their physiological determinants

Physiological basis of the trade-off between grain number (GN) and thousand grain weight (TGW) is key to improve wheat yield. To that end, three wheat line groups were assessed at conventional (300-350 pl m-2) and low (44 pl m-2) plant rates in the field: TaExpA6 (ectopic expression), TaGW2 (TaGW2 triple mutant), and TaP1xGW2A (VRT-A2 ectopic expression and TaGW2-A knock-out), together with their wild-types (WT). Except TaP1xGW2A, the manipulated lines increased TGW over their WTs. However, only the transgenic TaExpA6 line reached higher grain yield (GY) than its WT, whereas increased TGW recorded by the triple knockout of TaGW2 was fully compensated by reduced spike number (SpN) and grain number per spike (GNS). Contrasting effects of TaExpA6 and TaGW2 lines were found on the ovary weight and floret dynamics, associated with the trade-off between GW and GN. Interestingly, the overexpression of TaExpA6 gene acts in grain tissues at post-anthesis avoiding the overlap with GN determination, while TaGW2 disruption constrains tillering, likely as a pleiotropic effect, and shifts intra-spike resource allocation promoting early ovary growth at the expense of distal floret development and GNS. Low plant rate increased resource allocation to the spike, mitigating the GW-GNS trade-off and increasing both traits simultaneously.

plant biology↗

bioRxiv2024

The trade-off between grain weight and grain number in wheat is explained by the overlapping of the key phases determining these major yield components

Enhancing grain yield is a primary goal in the cultivation of major staple crops, including wheat. Recent research has focused on identifying the physiological and molecular factors that influence grain weight, a critical determinant of crop yield. However, a bottleneck has arisen due to the trade-off between grain weight and grain number, whose underlying causes remain elusive. In a novel approach, a wheat expansin gene, TaExpA6, known for its expression in root tissues, was engineered to express in the grains of the spring wheat cultivar Fielder. This modification led to increases in both grain weight and yield without adversely affecting grain number. Conversely, a triple mutant line targeting the gene TaGW2, a known negative regulator of grain weight, resulted in increased grain weight but decreased grain number, potentially offsetting yield gains. This study aimed to evaluate four wheat genotypes: (i) a transgenic line expressing TaExpA6, (ii) its wild-type counterpart (Fielder), (iii) a TaGW2 triple mutant line, and (iv) its wild-type. Conducted in southern Chile, the study employed a Complete Randomized Block Design with four replications, under well-managed field conditions including fertilization, irrigation, and pest control. The primary metrics assessed were grain yield, grain number, and average grain weight per spike, along with detailed measurements of grain weight and dimensions across the spike, and ovary weight at pollination (Waddingtons scale 10). The expression levels of TaExpA6 and TaGW2 were also monitored post-anthesis. Results indicated that both the TaExpA6 line and the triple mutant line achieved significantly higher average grain weights compared to their respective wild types. Notably, the TaExpA6 line did not exhibit a reduction in grain number, thereby enhancing grain yield per spike. In contrast, the triple mutant line showed a reduced grain number per spike, with no significant change in overall yield. Analysis of ovary size, grain weight dynamics, and gene expression patterns suggests that the trade-off between grain weight and number could be attributed to the overlapping of the critical periods for the determination of these traits.

plant biology↗