Abstract
The three most important agronomic traits of rice (Oryza sativa), yield, plant height, and flowering time, are controlled by many quantitative trait loci (QTLs). In this study, a newly identified QTL, DTH8 (QTL for days to heading on chromosome 8), was found to regulate these three traits in rice. Map-based cloning reveals that DTH8 encodes a putative HAP3 subunit of the CCAAT-box-binding transcription factor and the complementary experiment increased significantly days to heading, plant height, and number of grains per panicle in CSSL61 (a chromosome segment substitution line that carries the nonfunctional DTH8 allele) with the Asominori functional DTH8 allele under long-day conditions. DTH8 is expressed in most tissues and its protein is localized to the nucleus exclusively. The quantitative real-time PCR assay revealed that DTH8 could down-regulate the transcriptions of Ehd1 (for Early heading date1) and Hd3a (for Heading date3a; a rice ortholog of FLOWERING LOCUS T) under long-day conditions. Ehd1 and Hd3a can also be down-regulated by the photoperiodic flowering genes Ghd7 and Hd1 (a rice ortholog of CONSTANS). Meanwhile, the transcription of DTH8 has been proved to be independent of Ghd7 and Hd1, and the natural mutation of this gene caused weak photoperiod sensitivity and shorter plant height. Taken together, these data indicate that DTH8 probably plays an important role in the signal network of photoperiodic flowering as a novel suppressor as well as in the regulation of plant height and yield potential.
Highlights
The three most important agronomic traits of rice (Oryza sativa), yield, plant height, and flowering time, are controlled by many quantitative trait loci (QTLs)
As one of the most common promoter elements found in a large number of genes in animals, fungi, and plants, the CCAAT box is recognized by the HAP complex, which consists of three subunits: HAP2 (NF-YA/CBF-B), HAP3 (NF-YB/CBF-A), and HAP5 (NF-YC/CBF-C; Maity and de Crombrugghe, 1998; Mantovani, 1999)
Several chromosome segment substitution lines (CSSLs), such as CSSL8 and CSSL61, carrying a chromosome segment of IR24 on DTH8 under the Asominori genetic background, showed earlier heading and its plant height, number of grains per panicle, yield, and dry weight per plant decreased significantly in natural LD (NLD) condition compared with Asominori (Fig. 1; Table I; Supplemental Fig. S2; Supplemental Table S2), but no significant differences in these agronomic traits have been found in natural SD (NSD) conditions
Summary
The three most important agronomic traits of rice (Oryza sativa), yield, plant height, and flowering time, are controlled by many quantitative trait loci (QTLs). The transcription of DTH8 has been proved to be independent of Ghd and Hd1, and the natural mutation of this gene caused weak photoperiod sensitivity and shorter plant height. Taken together, these data indicate that DTH8 probably plays an important role in the signal network of photoperiodic flowering as a novel suppressor as well as in the regulation of plant height and yield potential. Our data showed that DTH8 suppressed rice flowering under LD conditions and we surmise that it probably plays an important role in the regulation of plant height and yield potential in rice
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