Analysis of the functions of TaGW2 homoeologs in wheat grain weight and protein content traits

Abstract

GW2 is emerging as a key genetic determinant of grain weight in cereal crops; it has three homoeologs (TaGW2-A1, -B1 and -D1) in hexaploid common wheat (Triticum aestivum L.). Here, by analyzing the gene editing mutants that lack one (B1 or D1), two (B1 and D1) or all three (A1, B1 and D1) homoeologs of TaGW2, several insights are gained into the functions of TaGW2-B1 and -D1 in common wheat grain traits. First, both TaGW2-B1 and -D1 affect thousand-grain weight (TGW) by influencing grain width and length, but the effect conferred by TaGW2-B1 is stronger than that of TaGW2-D1. Second, there exists functional interaction between TaGW2 homoeologs because the TGW increase shown by a double mutant (lacking B1 and D1) was substantially larger than that of their single mutants. Third, both TaGW2-B1 and -D1 modulate cell number and length in the outer pericarp of developing grains, with TaGW2-B1 being more potent. Finally, TaGW2 homoeologs also affect grain protein content as this parameter was generally increased in the mutants, especially in the lines lacking two or three homoeologs. Consistent with this finding, two wheat end-use quality-related parameters, flour protein content and gluten strength, were considerably elevated in the mutants. Collectively, our data shed light on functional difference between and additive interaction of TaGW2 homoeologs in the genetic control of grain weight and protein content traits in common wheat, which may accelerate further research on this important gene and its application in wheat improvement.

Development of an Agrobacterium‐delivered CRISPR/Cas9 system for wheat genome editing

“…CRISPR/Cas9 has been the primary choice for plant genome editing, and Agrobacterium ‐mediated transformation is the most common method for delivery of the CRISPR/Cas9 DNA components to plants (Soyars et al ., ). Mainly due to historical reason, all genome editing systems in wheat were implemented through the biolistics‐mediated transformation (Liang et al ., ; Sánchez‐León et al ., ; Wang et al ., , ; Zhang et al ., ,). Co‐transfer of large DNA fragments from the vector backbone by biolistic transformation leads to the high frequency of transgene silencing (Anand et al ., ; Tassy et al ., ).…”

“…In T 0 plants, deep sequencing indicates that over 99% of the mutations are due to deletions, and our genotyping data from T 1 and T 2 plants show that only five insertions were found of the 68 mutations detected, all of which are insertions of 1‐bp A or T. Remaining 63 mutations are deletions (Figure S11). Similar scenarios were also found in other wheat studies (Liang et al ., ; Sánchez‐León et al ., ; Wang et al ., , ; Zhang et al ., ,). Thus, deletions are the dominant type of edit mutations in wheat.…”

“…In addition to TaCKX2‐1 , we also obtained mutation in three other grain regulatory genes, TaGLW7 , TaGW2 , and TaGW8 . Two recent studies on TaGW2 showed that knockout mutations of this gene could significantly increase wheat grain size and grain weight (Wang et al ., ; Zhang et al ., ,). Combining and transferring the mutations of TaCKX2‐1 and TaGW2 into the elite wheat cultivars are expected to have an additive effect on increasing the sink strength.…”

“…In this respect, the CRISPR technology is expected to contribute greatly to creating novel variations in wheat. Wheat was one of the plant species first modified by CRISPR/Cas9 (Shan et al ., ), and several traits have been targeted for mutations, including powdery mildew resistance (Wang et al ., ), grain size (Wang et al ., ; Zhang et al ., ), and grain quality (Liang et al ., ; Sánchez‐León et al ., ; Zhang et al ., ). In all these researches, the Cas9 and sgRNA transgenes were delivered by the biolistic bombardment.…”

A reductionist approach to dissecting grain weight and yield in wheat

“…GW2 is an E3 ubiquitin ligase that negatively regulates grain width, and this mechanism appears to be conserved across species, including wheat, Arabidopsis and maize, on both a cellular and molecular level (Li et al ; Xia et al ; Simmonds et al ). The wheat ortholog, TaGW2 , was shown to affect cell number in maternal tissue and to have ubiquitination activity, as in rice and Arabidopsis (Bednarek et al ; Xia et al ; Dong et al ; Zhang et al ).…”