Rice Flowering Locus T 1 plays an important role in heading date influencing yield traits in rice

Abstract

Important role of flowering genes in enhancing grain productivity in rice has become well recognized for a number of key genes regulating the florigen production, but little has been known for the two florigen genes themselves. In this study, pleiotropism of Rice Flowering Locus T 1 (RFT1), one of the two florigen genes in rice, was firstly evaluated using near isogenic lines (NILs) carrying RFT1 alleles from the indica rice cultivars Zhenshan 97 (ZS97) and Milyang 46, respectively, and then determined by transformation of the RFT1 ^ZS97 allele into a japonica rice variety, Zhonghua 11. The RFT1 ^ZS97 allele was shown to delay heading and increase plant height, grain weight, grain number and grain yield, indicating that RFT1 plays an important role in the growth and development of rice. This study has also validated the potential of using a new type of genetic resource, sequential residual heterozygotes (SeqRHs), for QTL fine-mapping. A step-by-step approach was employed for SeqRHs identification, NIL development and QTL fine-mapping. The heterozygous segments and candidate QTL regions were gradually narrowed down. Eventually, the QTL region was delimited to a 1.7 kb region containing a single gene.

Figure 1

The procedure used for fine-mapping qHd6 in this study. A three-step procedure, selecting RHs overlapped in the candidate QTL region – constructing NIL-F₂ populations – performing QTL analysis, was repeated until the QTL was placed at the RFT1 locus. NIL, near isogenic line. RH, residual heterozygote.

Figure 2

Heading date segregation of the three NIL-F₂ populations firstly used in this study. (a) Distribution of heading date and its association with the three genotypic groups in each population. (b) Segregating regions of the three populations and the 96.4-kb region mapped for qHd6. The three populations are each constructed from selfed seeds of an RH plant in F₉ which is a progeny of an F₇ plant of the indica rice cross ZS97/MY46. Pedigree refers to the pedigree of the residual heterozygote that was selfed to produce the NIL-F₂ population, in which the first and second numbers are the Plant No. in F₈ and F₉, respectively. n, number of plants.

Figure 3

Segregating regions of four sets of NIL-F₂ populations. (a) Three populations in F₁₁ used to validate the location and effect of qHd6 disclosed in the previous generation. (b) Three populations in F₁₂ used to delimitate qHd6 into a 62.1-kb region. (c) Six populations in F₁₄ used to delimitate qHd6 into a 29.9-kb region. (d) Two populations in F₁₆ used to place qHd6 at the RFT1 locus and to construct NILs for analyzing the RFT1 pleiotropism. Pedigree refers to the pedigree of the residual heterozygote that was selfed to produce the NIL-F₂ population, in which the first number is the Plant No in F₈, followed by those in later generations up to F₁₀, F₁₁, F₁₃ and F₁₅ in (a,b,c and d), respectively. n, number of plants.