Is the time of anthesis in rice (Oryza sativa) influenced by photoperiod?

Photoperiod sensitivity in rice cultivars is defined when the cultivar begins anthesis on a relatively invariant date, varying by < 7 days, regardless of the date of sowing or germination. While the date of flowering in photoperiod sensitive (PPS) rice cultivars is characteristically determined by the day length, especially during the short-day season (September-December), the response of the flower opening time (FOT) to photoperiod remains hitherto unexplored. This paper examines whether day length restrains year-to-year variation in FOT in PPS cultivars. We examined 105 PPS and 173 photoperiod insensitive (PPI) cultivars grown in different years and estimated their year-to-year FOT difference (or FOTD) and the year-to-year difference of sunrise to anthesis duration (or SADD). Wilcoxon signed rank test and bootstrap test were then performed to test whether these descriptors significantly differed between PPS and PPI groups of cultivars. The means of FOTD and SADD were detected to be significantly less in the PPS group than in the PPI group of cultivars, indicating significantly lesser variability of FOT in PPS than in PPI cultivars. This is the first report of a strong restraining influence of photoperiod on FOT variability in PPS cultivars.

Structural and functional analysis of CCT family genes in pigeonpea

BACKGROUND

Pigeonpea (Cajanus cajan L.) is a photoperiod-sensitive short-day plant. Understanding the flowering-related genes is critical to developing photoperiod insensitive cultivars.

METHODS

The CCT family genes were identified using 'CCT DOMAIN PROTEIN' as a keyword and localized on the chromosomes using the BLAST search option available at the LIS database. The centromeric positions were identified through BLAST search using the centromeric repeat sequence of C. cajan as a query against the chromosome-wise FASTA files downloaded from the NCBI database. The CCT family genes were classified based on additional domains and/or CCT domains. The orthologous and phylogenetic relationships were inferred using the OrthoFinder and MEGA 10.1 software, respectively. The CCT family genes' expression level in photoperiod-sensitive and insensitive genotypes was compared using RNA-seq data and qRT-PCR analysis.

RESULTS

We identified 33 CCT family genes in C. cajan distributed on ten chromosomes and nine genomic scaffolds. They were classified into CMF-type, COL-type, PRR-type, and GTCC- type. The CCT family genes of legumes exhibited an extensive orthologous relationship. Glycine max showed the maximum similarity of CCT family genes with C. cajan. The expression analysis of CCT family genes using photoperiod insensitive (ICP20338) and photoperiod sensitive (MAL3) genotypes of C. cajan demonstrated that CcCCT4 and CcCCT23 are the active CONSTANS in ICP20338. In contrast, only CcCCT23 is active in MAL3.

CONCLUSION

The CCT family genes in C. cajan vary considerably in structure and domain types. They are maximally similar to soybean's CCT family genes. The differential photoperiod response of pigeonpea genotypes, ICP20338 and MAL3, is possibly due to the difference in the number and types of active CONSTANS in them.

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

BACKGROUND

Methyl-CpG-binding domain (MBD) proteins play important roles in epigenetic gene regulation, and have diverse molecular, cellular, and biological functions in plants. MBD proteins have been functionally characterized in various plant species, including Arabidopsis, wheat, maize, and tomato. In rice, 17 sequences were bioinformatically predicted as putative MBD proteins. However, very little is known regarding the function of MBD proteins in rice.

RESULTS

We explored the expression patterns of the rice OsMBD family genes and identified 13 OsMBDs with active expression in various rice tissues. We further characterized the function of a rice class I MBD protein OsMBD707, and demonstrated that OsMBD707 is constitutively expressed and localized in the nucleus. Transgenic rice overexpressing OsMBD707 displayed larger tiller angles and reduced photoperiod sensitivity-delayed flowering under short day (SD) and early flowering under long day (LD). RNA-seq analysis revealed that overexpression of OsMBD707 led to reduced photoperiod sensitivity in rice and to expression changes in flowering regulator genes in the Ehd1-Hd3a/RFT1 pathway.

CONCLUSION

The results of this study suggested that OsMBD707 plays important roles in rice growth and development, and should lead to further studies on the functions of OsMBD proteins in growth, development, or other molecular, cellular, and biological processes in rice.

Combined transcriptome sequencing reveals the photoperiod insensitivity mechanism of oats

Avena sativa L. is the most important cultivated oat species worldwide. Although photoperiod-insensitive oat varieties exist, the molecular mechanisms underlying their photoperiod sensitivity are poorly understood. This study investigated the effects of day length on the fioral transition of oats and the mechanisms underlying oat photoperiod insensitivity. Photoperiod-sensitive and photoperiod-insensitive varieties, including gp012, were used in shading experiments, and the developing leaves and main shoot apices (MSAs) of the HONGQI2 and gp012 varieties were used for sequencing. Leaves and MSAs were collected in 2016, and their transcriptomes were sequenced. The photoperiod-insensitive varieties headed under both short-day and long-day conditions, while the photoperiod-sensitive varieties headed only under long-day conditions. A total of 60673 transcript sequences were obtained, 7932 of which were differentially expressed; 3194 and 4738 transcripts were differentially expressed in the leaves and MSAs, respectively. A total of 25793 transcripts were classified into 123 pathways based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. The carbon metabolism pathways were dominant, followed by ribosome and protein processing in the endoplasmic reticulum. In addition, 203 transcripts were classified into the circadian rhythm pathway. Compared with the expression of pseudo-response regulator protein 37 (PRR37) in photoperiod-sensitive varieties, that in photoperiod-insensitive varieties was upregulated. Among the differentially expressed transcripts (DETs), 8 MADS-box genes were identified. PRR37 is a key regulator of oat photoperiod insensitivity. The obtained transcriptome dataset may provide a reference for analyzing oat transcript expression, and the results should be used as a reference for oat breeding and production.

Ghd8 controls rice photoperiod sensitivity by forming a complex that interacts with Ghd7

BACKGROUND

Flowering time is one of the most important agronomic characteristics that ultimately determine yield potential and eco-geographical adaptation in crops. Ghd8 and Ghd7, two major flowering genes, have similar functions and large pleiotropic effects in controlling the heading date, plant height and grain yield of rice. However, these gene interactions at the genetic and molecular levels have not been determined to date.

RESULTS

In this study, we investigated the genetic interaction between Ghd8 and Ghd7 by using a set of near-isogenic lines and a panel of natural germplasm accessions in rice. We found that Ghd8 affected multiple agronomic traits in a functional Ghd7-dependent manner. Both functional Ghd8 and Ghd7 are pivotal for rice photoperiod sensitivity controlled by Hd1 and Hd3a. GHD8 could form a heterotrimeric complex with HD1 and OsHAP5b to activate the transcription of Ghd7 by binding directly to the promoter region of Ghd7, which contains the CCAAT-box motif.

CONCLUSIONS

The results of this study help to elucidate the genetic and molecular bases of Ghd8 and Ghd7 interactions, indicating that Ghd8 acts upstream of Ghd7 to activate its transcription, which inhibits Hd3a expression and thus affects flowering time and rice adaptation.

Photoperiod sensitivity of Canadian flax cultivars and 5-azacytidine treated early flowering derivative lines

BACKGROUND

Early flowering and maturing flax (Linum usitatissimum L.) cultivars are better adapted than lines with a longer reproductive phase for the short growing season of the northern Canadian Prairies. We examined the role of long days (LD) and short days (SD) on the time taken to flower in five established flax cultivars and three mutant-derived F₁₀ lines. The photoperiod sensitivity of these eight different genotypes was determined using a reciprocal transfer experiment involving weekly transfers between LD and SD environments.

RESULTS

The genotypes tested had varying degrees of photoperiod sensitivity and demonstrated reduced time to flowering if exposed to LD environments prior to a critical time point. The duration of each of the three phases of vegetative growth differed among the genotypes studied. Transfers from SD to LD shortened the vegetative stage, reduced time to flowering, and extended the reproductive phase in the genotypes studied. Mutant-derived lines RE1/2/3 flowered significantly earlier compared to CDC Sorrel, CDC Bethune, Flanders, Prairie Thunder, and Royal. Modelling of the flowering times indicated that transferring the cultivars from SD to LD increased the photoperiod sensitive time; however, different reproductive phases for mutant lines were not defined as parsimonious models were not identified. Expression of the putative flax homologs for CONSTANS (CO), FLOWERING LOCUS T (FT), and GIGANTEA (GI) was examined in the leaves of Royal and RE1/2/3 plants at 10, 15, 19 and 29 days after planting. Expression of putative FT homologs was detected in all three early-flowering lines but expression was negligible, or not detected, in Royal.

CONCLUSIONS

Models defining the three phases of reproductive development were established for the five cultivars studied; however, it was not possible to identify these phases for the three early flowering and photoperiod insensitive epimutant-derived lines. A putative flax homolog of FT, a key regulator of flowering time, is more highly expressed in RE plants, which may condition the day-length insensitivity in the early flowering 'epimutant' lines.

Features of Ppd-B1 expression regulation and their impact on the flowering time of wheat near-isogenic lines

BACKGROUND

Photoperiod insensitive Ppd-1a alleles determine early flowering of wheat. Increased expression of homoeologous Ppd-D1a and Ppd-A1a result from deletions in the promoter region, and elevated expression of Ppd-B1a is determined by an increased copy number.

RESULTS

In this study, using bread wheat cultivars Sonora and PSL2, which contrast in flowering time, and near-isogenic lines resulting from their cross, "Ppd-m" and "Ppd-w" with Ppd-B1a introgressed from Sonora, we investigated the putative factors that influence Ppd-B1a expression. By analyzing the Ppd-B1a three distinct copies, we identified an indel and the two SNPs, which distinguished the investigated allele from other alleles with a copy number variation. We studied the expression of the Ppd-A1, Ppd-B1a, and Ppd-D1 genes along with genes that are involved in light perception (PhyA, PhyB, PhyC) and the flowering initiation (Vrn-1, TaFT1) and discussed their interactions. Expression of Ppd-B1a in the "Ppd-m" line, which flowered four days earlier than "Ppd-w", was significantly higher. We found PhyC to be up-regulated in lines with Ppd-B1a alleles. Expression of PhyC was higher in "Ppd-m". Microsatellite genotyping demonstrated that in the line "Ppd-m", there is an introgression in the pericentromeric region of chromosome 5B from the early flowering parental Sonora, while the "Ppd-w" does not have this introgression. FHY3/FAR1 is known to be located in this region. Expression of the transcription factor FHY3/FAR1 was higher in the "Ppd-m" line than in "Ppd-w", suggesting that FHY3/FAR1 is important for the wheat flowering time and may cause earlier flowering of "Ppd-m" as compared to "Ppd-w".

CONCLUSIONS

We propose that there is a positive bidirectional regulation of Ppd-B1a and PhyC with an FHY3/FAR1 contribution. The bidirectional regulation can be proposed for Ppd-A1a and Ppd-D1a. Using in silico analysis, we demonstrated that the specificity of the Ppd-B1 regulation compared to that of homoeologous genes involves not only a copy number variation but also distinct regulatory elements.