Exploring natural allelic variations of the β-triketone herbicide resistance gene HIS1 for application in indica rice and particularly in two-line hybrid rice

Abstract

Background: Benzobicyclon (BBC) is a β-triketone herbicide (bTH) used in rice paddy fields. It has the advantages of high efficiency, low toxicity, high crop safety, and good environmental compatibility, and shows efficacy against paddy weeds resistant to other types of herbicides. However, as some important indica rice varieties are susceptible to BBC, BBC is currently only registered and applied in japonica rice cultivation areas.Results: By analyzing haplotypes of the bTHs broad-spectrum resistance gene HIS1 and phenotypes for BBC in 493 major indica rice accessions in China, we identified a novel non-functional allelic variant of HIS1 in addition to the previously reported 28-bp deletion. Through detection with markers specific to the two non-functional mutations, it was clear that 25.4% of indica conventional varieties, 59.9% of fertility restorers, and 15.9% of sterile lines were susceptible to BBC. In addition, due to natural allelic variations of the HIS1 gene in the sterile and restorer lines, some two-line hybrid sterile lines were sensitive to bTHs, and the corresponding restorers were resistant. We showed the potential effectiveness of using bTHs to address the issue of two-line hybrid rice seed purity stemming from the self-crossing of sterile lines during hybrid rice seed production. Finally, allelic variations of the HIS1 gene may also play an important role in the mechanized seed production of hybrid rice.Conclusions: Our findings offer guidance for the application of BBC in indica rice areas and provide a non-transgenic approach to address the seed purity issue of two-line hybrid rice.

Benzobicyclon efficacy is affected by plant growth stage, HPPD Inhibitor Sensitive 1 (HIS1) expression and zygosity in weedy rice (Oryza sativa)

“…As predicted, his1/his1 accessions/cultivars were highly sensitive to benzobicyclon at 371 g ha −1 regardless of growth stage, and predominantly HIS1 accessions or HIS1/HIS1 cultivars (e.g., LaKast) at the ≥5-leaf growth stage were tolerant. These statements are supported by evidence in the literature (Akasaka et al 2011;Kwon et al 2012;Lv et al 2021;Maeda et al 2019;Young et al 2017). For HIS1/his1 accessions/cultivars, the model predicted severe suppression to complete control at ≤2-leaf growth stage, which was observed at the Pine Tree location, but the model would indicate greater control at the 5-leaf growth stage.…”

“…Benzobicyclon is a 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide that has activity on a wide range of aquatic, grass, sedge, and broadleaf weeds in flooded rice (Oryza sativa L.) fields (Sekino et al 2008). Tolerance in rice can vary depending on the genetic background of each cultivar, but in general, japonica cultivars exhibit tolerance to benzobicyclon, while most but not all indica cultivars are sensitive (Kwon et al 2012;Lv et al 2021;Maeda et al 2019;Young et al 2018). The HPPD Inhibitor Sensitive 1 (HIS1) gene is responsible for tolerance in rice, which is conferred through hydroxylation of benzobicyclon hydrolysate (active parent) into a less phytotoxic compound and not benzobicyclon (proform) (Maeda et al 2019).…”

“…The HPPD Inhibitor Sensitive 1 (HIS1) gene is responsible for tolerance in rice, which is conferred through hydroxylation of benzobicyclon hydrolysate (active parent) into a less phytotoxic compound and not benzobicyclon (proform) (Maeda et al 2019). Sensitivity in indica cultivars is either the result of a loss-of-function frameshift mutation (28-bp deletion) resulting in truncated protein (Maeda et al 2019) or a missense mutation located in the region of the putative substrate pocket that encodes for a glycine instead of a valine at the 286th (Val-286-Gly) amino acid position (Lv et al 2021). Hereafter, a less than fully functional HIS1 allele with either mutation will be referred to as his1.…”