In-Frame and Frame-Shift Editing of the Ehd1 Gene to Develop Japonica Rice With Prolonged Basic Vegetative Growth Periods

Abstract

Japonica rice has become increasingly popular in China owing to its superior grain quality. Over the past decades, "indica to japonica" projects have been proposed to promote cultivation of japonica rice in low latitudes in China. Traditionally, japonica varieties were planted mainly in mid latitudes in the northeast plain and Yangtze River region. The key obstacle for introducing elite mid-latitude japonica varieties to low latitudes is the severe shortening of growth period of the japonica varieties due to their sensitivity to low-latitude short photoperiod and high temperature. Here we report development of new japonica rice with prolonged basic vegetative growth (BVG) periods for low latitudes by targeted editing the Early heading date 1 (Ehd1) gene. Using CRISPR/Cas9 system, we generated both frame-shift and/or in-frame deletion mutants in four japonica varieties, Nipponbare, Longdao16, Longdao24, and Xiushui134. When planting at low-latitude stations, the frame-shift homozygous lines exhibited significantly longer BVG periods compared with wild-types. Interestingly, we observed that minor deletion of the first few residues within the receiver domain could quantitatively impair the function of Ehd1 on activation of Hd3a and RFT1, resulting in an intermediatelong BVG period phenotype in the homozygous in-frame deletion ehd1 lines. Field investigation further showed that, both the in-frame and frame-shift lines exhibited significantly improved yield potential compared with wild-types. Our study demonstrates an effective approach to rapid breeding of elite japonica varieties with intermediate-long and long BVG periods for flexible cropping systems in diverse areas or under different seasons in southern China, and other low-latitude regions.

Overexpression of a methyl-CpG-binding protein gene OsMBD707 leads to larger tiller angles and reduced photoperiod sensitivity in rice

“…However, no other known tiller angle regulator genes were identified as DEGs. Notably, a number of genes with functions in controlling flowering time were identified among the DEGs, including FLAVIN-BINDING, KELCH REPEAT, F-Box 1 ( OsFKF1 ) [ 31 ], Early heading date1 ( Ehd1 ) [ 32 , 33 ], Days to heading on chromosome 2 ( DTH2 ) [ 34 ], Heading date3a ( Hd3a ) and RICE FLOWERING LOCUS T1 ( RFT1 ) [ 35 , 36 ], OsMADS14 and OsMADS15 [ 37 ], and Flowering Locus T gene homologs FT-L7 , FT-L8 and FT-L12 that promote flowering, and Grain number, plant height, and heading date2 ( GHd2 ) [ 38 ] that inhibits flowering. Under SD, Hd3a , RFT1 , FT-L7 , OsMADS14 , and OsMADS15 were down-regulated in OX707-#21.…”

Gene editing applications to modulate crop flowering time and seed dormancy

“…The in-frame mutants exhibited intermediate-long vegetative growth periods. The field trials showed that both the in-frame and frame-shift mutant lines had significantly improved yield compared with wild-type plants, demonstrating the potential of proposed gene editing approach for adapting elite Japonica varieties for production in low latitude (Wu et al 2020).…”

“…A recent study by Wu et al (2020) targeted the Ehd1 gene itself with the aim to adapt Japonica rice, traditionally cultivated in the mid-latitude area to the lower latitude of Southern China. The mid-latitude Japonica varieties, which increase popularity over Indica because of their superior grain quality, commonly display early flowering when growing under short-day photoperiod and high temperature in low latitudes, resulting in low grain yield because of shortened vegetative growth period (Wei et al 2016).…”

CRISPR/Cas: a Nobel Prize award-winning precise genome editing technology for gene therapy and crop improvement

“…Double CRISPR knock-out of TaGW2 showed a stronger effect on these traits than a single mutation ( Zhang Y et al, 2018 ). By targeted editing of the early heading date 1 ( Ehd1 ) gene by CRISPR/Cas9, Wu et al (2020) generated both frame-shift and in-frame deletion mutants in four rice cultivars. The mutants showed significantly longer basic vegetative growth periods and significantly improved yield potential compared with wild types when planted at low-latitude stations.…”