The outstanding rooting1 mutation gene maintains shoot growth and grain yield through promoting root development in rice under water deficit field environments

Abstract

Drought is one of the most serious constraints to rice cultivation, even under alternate wetting and drying (AWD), which is a water-saving management practice. In rice, enhanced root development is essential for stable shoot growth, adaptability and productivity under water deficit environments. We identified and characterized outstanding rooting1 (our1) rice mutant using hydroponics. The present study sought to examine morphological root traits of the our1 mutant and the role of the mutation gene in shoot growth and yield under AWD. Thus, we evaluated the growth performance of the our1 rice mutant in pot experiments and under field AWD conditions in Kenya. The experiments were conducted with our1 mutant, its wild type and their progenies under both AWD and continuously waterlogged (CWL) conditions. The our1 mutant possessed a well-developed root system and exhibited particularly enhanced thin root development, which was maintained from the early vegetative stage through the reproductive stage under both pot and field AWD management. This enhanced root development promoted shoot growth through increased water uptake during rewatered conditions between drought periods in AWD. In addition, the our1 mutant showed enhanced shoot growth during the reproductive stage, resulting in the maintenance of yield under AWD fields. Genotypes harbouring our1 mutation gene showed higher yields compared to wild-type genotypes which was attributed to their higher photosynthetic ability as a result of enhanced root activity. These results suggest the important role of a well-developed root system architecture and enhanced root function in stabilizing rice yields under water-limited environments. Our findings indicate that the our1 mutation gene can serve as a novel breeding material to mitigate the impact of transient drought stress on yield under AWD.

OsbZIP1 regulates phosphorus uptake and nitrogen utilization, contributing to improved yield

“…OsbZIP48 knock‐down lines produced by RNAi technology were reported as slightly taller than WT in the greenhouse, however, their yield was not calculated (Burman et al., 2018). In a recent report, an OsbZIP1 mutant, outstanding root1 ( our1 ) with altered root architecture also showed high yield under water‐limited environments (Hasegawa, Wainaina, et al., 2021). To our knowledge, our report is the first to show the function of a rice HY5 homolog in the uptake of nutrients, such as P and N.…”

“…In the field test, 88n showed longer and larger panicles than WT (Figure 5b). In a previous report, the rice our1 ( osbzip1 ) mutant also showed longer panicles than WT (Hasegawa, Wainaina, et al., 2021). A. thaliana hy5 mutant also showed elongated hypocotyl under light conditions (Oyama et al., 1997).…”

“…OsbZIP1 is a homolog of A. thaliana HY5 , a positive regulator of photomorphogenesis (Oyama et al., 1997) and encodes a basic leucine zipper (bZIP) transcription factor. There are three HY5 homologs in the rice genome, OsbZIP1 , OsbZIP18 and OsbZIP48 (Figure S1b, Burman et al., 2018; Hasegawa, Lucob‐Agustin, et al., 2021; Hasegawa, Wainaina, et al., 2021). The transcript bearing a 9 bp deletion is expected to be translated to an OsbZIP1 protein with a three amino acid deletion in the leucine zipper domain that is conserved between A. thaliana HY5 and the rice HY5 homologs (Figure S1c,d).…”

“…This G to A nucleotide substitution was located at the splicing site of OsbZIP1 and produce two types of OsbZIP1 transcripts in 88n, one being an intron read through with an early stop codon, the other bearing a 9 bp deletion in exon 2 (Figure 3a; Figure S1c,d). OsbZIP1 is a homolog of A. thaliana HY5, a positive regulator of photomorphogenesis (Oyama et al, 1997) homologs in the rice genome, OsbZIP1, OsbZIP18 and Osb-ZIP48 (Figure S1b, Burman et al, 2018;Hasegawa, Wainaina, et al, 2021).…”