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Effect of the light and dark conditions on flower opening time between cultivated rice (Oryza sativa) and a near-isogenic early-morning flowering line.

ABSTRACT: Flower opening time (FOT) is affected by genetic and environmental factors, but little is known about the effect of light and dark conditions on FOT in cereal crops. FOT of an indica rice cultivar, IR64, and its near-isogenic line carrying a QTL for an early-morning flowering trait (IR64+qEMF3) were investigated in a natural-light and temperature-controlled small greenhouse by exposing either the panicle or stem or both plant organs to different light and dark conditions. FOT did not change in either genotype when panicles were exposed to light. A large difference in FOT was found between genotypes when panicles were exposed to dark conditions; no flower opening was observed in IR64, whereas flower opening was delayed but observed in IR64+qEMF3. These results suggest that the panicle is the organ that perceives light for flower opening in both genotypes, whereas the light requirement to reach flower opening was quite different between genotypes. Flower opening of IR64 occurred concomitantly with elongation of anther filament in the light after the dark treatment stopped, whereas approximately half of flowering of IR64+qEMF3 resulted in apparent cleistogamy even during dark treatment. An extended duration of the dark treatment until 1730H (30-50 min before sunset) made FOT of IR64 spikelets on the next day shifted to a time as early as that of IR64+qEMF3, with significant advancement of FOT compared to the control IR64 spikelets. Our results indicated that different flowering responses to light and dark conditions exist between IR64 and IR64+qEMF3. These findings provide clues for understanding the unique genetic controls of flowering in an EMF line in rice. This study also showed evidence that artificial light environments can shift the FOT of IR64 to that of IR64+qEMF3.

SUBMITTER: Ishimaru T

PROVIDER: S-EPMC8300546 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:In spite of short-day (SD) nature, rice (Oryza sativa) shares a conserved photoperiodic network for flowering control with long-day plants like Arabidopsis thaliana. Flowering or heading is an important agronomic trait in rice. NAC transcription factors (TFs) are well-conserved and one of the largest families of plant TFs. However, their function in flowering or heading time is not well-known yet. A preferential expression of a membrane-bound NAC-like TF OsNTL5 in developing leaves and panicles of rice indicated to us its putative role in flowering. To examine its function, three independent constructs was generated, one with a deletion in the C terminus membrane-spanning domain (OsNTL5?C), OsNTL5?C fused with the SRDX transcriptional repressor motif and OsNTL5?C used with the VP16 activation domain under the Ubiquitin promoter to produce the overexpressing lines OsNTL5?C, OsNTL5?C-SRDX, and OsNTL5?C-VP, respectively in rice. The OsNTL5?C-VP line showed an early-flowering phenotype. In contrast to this, the plants with OsNTL5?C and OsNTL5?C-SRDX showed a very strong late-flowering phenotype, suggesting that OsNTL5 suppresses flowering as a transcriptional repressor. The protein subcellular localization assay suggested that N-terminal part of the OsNTL5 is localized to the nucleus after the protein is cleaved from its membrane-spanning domain at the C-terminal end and functions as a TF. Expression of flowering genes responsible for day length signals such as Early Heading Date 1 (Ehd1), Heading Date 3a (Hd3a), and Rice Flowering Locus T1 (RFT1) was significantly changed in the overexpression lines of OsNTL5?C-VP, OsNTL5?C, and OsNTL5?C-SRDX as analyzed by Quantitative Real-time PCR. ChIP-qPCR and rice protoplasts assays indicate that OsNTL5 directly binds to the promoter of Ehd1 and negatively regulates the expression of Ehd1, which shows antagonistic photoperiodic expression patterns of OsNTL5 in a 24-h SD cycle. Hence in conclusion, the NAC-like TF OsNTL5 functions as a transcriptional repressor to suppress flowering in rice as an upstream factor of Ehd1.

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Effect of the light and dark conditions on flower opening time between cultivated rice (Oryza sativa) and a near-isogenic early-morning flowering line.

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