Dynamic Analysis of QTLs on Plant Height with Single Segment Substitution Lines in Rice

Dynamic regulation of QTLs remains mysterious. Single segment substitution lines (SSSLs) and conditional QTL mapping and functional QTL mappings are ideal materials and methods to explore dynamics of QTLs for complex traits. This paper analyzed the dynamics of QTLs on plant height with SSSLs in rice. Five SSSLs were verified with plant height QTLs first. All five QTLs had significant positive effects at one or more developmental stages except QTL1. They interacted each other, with negative effects before 72 d after transplanting and positive effects since then. The five QTLs selectively expressed in specific periods, mainly in the periods from 35 to 42 d and from 49 to 56 d after transplanting. Expressions of epistasis were dispersedly in various periods, negative effects appearing mainly before 35 d. The five QTLs brought the inflexion point ahead of schedule, accelerated growth and degradation, and changed the peak plant height, while their interactions had the opposite effects. The information will be helpful to understand the genetic mechanism for developmental traits.

Dynamic Mapping Based on Single Segment Substitution Lines for Plant Height in Rice

Background: Dynamic regulations of QTLs still remain mysterious. Single segment substitution lines and conditional QTL mapping, functional QTL mappings are ideal materials and methods to explore epistatic interactions, expression patterns and functions of QTLs for complex traits.Results: Based on single segment substitution lines five QTLs on plant height in rice were identified first in this paper, and then their epistatic interactions, expression patterns and functions were systemmatically studied by tailing after each QTL. Unconditional QTL mapping showed the five QTLs were with significant effects at one or more stages, all of which increased plant height except QTL1. They interacted each other as homeostatic mechanisms to regulate plant height with negative effects before 72d after transplanting and positive since then. Conditional QTL mapping revealed the expression quantities and periods for the five QTLs and their epistases. Temporal expression pattern was verified again by selective expressions of QTLs in specific periods. QTL1 expressed negatively while QTL2 and QTL4 positively, mainly occurring in the periods from 35 to 42d and from 49 to 56d after transplanting. Epistatic expressions were dispersedly in various periods, mainly with negative effects before 35d while positive since then. Functional QTL mapping discovered the five QTLs brought the inflexion point ahead of schedule, accelerated the growth and the degradation, and changed the peak of plant height, while their interactions had the opposite effects approximately. This paper uncovered the dynamic rules of five QTLs and their interactions on plant height systematically, which will be helpful to understand the genetic mechanism for developmental traits.Conclusions: Five single segment substitution lines were tested with significant additive, dominant and epistatic effects of QTLs on plant height. Additive and dominant expressions were mainly in two periods, while epistasis dispersedly. The five QTLs and their interactions significantly regulated the developmental trajectory of plant height.

Identification, Pyramid and Candidate gene of QTL for Yield-related Traits Based on Rice CSSLs in Indica Xihui18 Background

Chromosome segment substitution line (CSSL) in rice is important for functional analysis and design breeding of target genes. Here, a novel rice CSSL-Z431 was identified from indica restorer line Xihui18 as recipient and Huhan3 as donor. Z431 contained six segments from Huhan3, with an average substitution length of 2.12 Mb. Compared with Xihui18, Z431 increased panicles per plant (PN) and displayed short-wide grains. The short-wide grain of Z431 were caused by reducing of cell length and increasing of cell width in the glume. Then, thirteen QTLs were identified in a secondary F2 population derived from Xihui18/Z431. Among them, six QTLs (qPN3, qGL3, qGW5, qRLW2, qRLW3, qGWT-5-2) were validated by four single-segment substitution lines (SSSLs, S1-S4) developed in F3. In addition, thirteen QTLs (qPN1, qPN2, qPL1, qPL2, qGPP1, qGPP2, qGL2, qGW1, qGW2, qGW3, qRLW5-2, qRLW1, qGWT2) were detected by these SSSLs, while not be identified in the F2 population from Xihui18/Z431. Increase of panicles per plant in Z431 was controlled by qPN3, qPN1 and qPN2. OsIAGLU should be the candidate gene for qPN3 by DNA sequencing. The short-wide grain of Z431 was controlled by qGL3, qGL2, qGW5, qGW2 and qGW3. By sequencing between Xihui18 and according SSSL, three candidate genes for qGL3 and two candidate genes for qGW5 were identified, respectively. In addition, pyramid of different QTLs (qPN1and qPN3; qPN2 and qPN3 etc.) yielded different epistatic effects. These results lay good foundation in molecular mechanism analysis of unreported genes and rice molecular design breeding.

Fine mapping of two grain chalkiness QTLs sensitive to high temperature in rice

Background Grain chalkiness is one of important factors affected rice grain quality. It is known that chalkiness is affected by the high temperature during the seed filling period. Although a larger of QTLs for chalkiness were reported across all 12 chromosomes, only a few of the QTLs were fine mapped or cloned up to now. Here, we fine map two QTLs for chalkiness in two single-segment substitution lines (SSSLs), 11–09 with substitution segment from O. sativa and HP67–11 with substitution segment from O. glaberrima. Results The grain chalkiness of SSSLs 11–09 and HP67–11 was significantly lower than that in the recipient Huajingxian 74 (HJX74) in consecutive 8 cropping seasons. The regression correlation analysis showed that percentage of chalky grain (PCG) and percentage of chalky area (PCA) were significantly and positively correlated with percentage of grain chalkiness (PGC). Two QTLs for grain chalkiness were located on two chromosomes by substitution mapping. qPGC9 was mapped on chromosome 9 with an estimated interval of 345.6 kb. qPGC11 was located on chromosome 11 and delimited to a 432.1 kb interval in the O. sativa genome and a 332.9 kb interval in the O. glaberrima genome. qPGC11 is a QTL for grain chalkiness from O. glaberrima and was mapped in a new region of chromosome 11. The effect of two QTLs was incomplete dominance. The additive effects of two QTLs on chalkiness in second cropping season (SCS) were significantly greater than that in first cropping season (FCS). Conclusions qPGC11 is a new QTL for grain chalkiness. The two QTLs were fine mapped. The donor alleles of qPGC9 and qPGC11 were sensitive to the high temperature of FCS.

Unconditional and conditional analysis of epistasis between tillering QTLs based on single segment substitution lines in rice

Epistasis plays an important role in manipulating rice tiller number, but epistatic mechanism still remains a challenge. Here we showed the process of epistatic analysis between tillering QTLs. A half diallel mating scheme was conducted based on 6 single segment substitution lines and 9 dual segment pyramiding lines to allow the analysis of 4 epistatic components. Additive-additive, additive-dominance, dominance-additive, and dominance-dominance epistatic effects were estimated at 9 stages of development via unconditional QTL analysis simultaneously. Unconditional QTL effect (QTL cumulative effect before a certain stage) was then divided into several conditional QTL components (QTL net effect in a certain time interval). The results indicated that epistatic interaction was prevalent, all QTL pairs harboring epistasis and one QTL always interacting with other QTLs in various component ways. Epistatic effects were dynamic, occurring mostly within 14d and 21–35d after transplant and exhibited mainly negative effects. The genetic and developmental mechanism on several tillering QTLs was further realized and perhaps was useful for molecular pyramiding breeding and heterosis utilization for improving plant architecture.

Analysis of QTL for Grain Size in a Rice Chromosome Segment Substitution Line Z1392 with Long Grains and Fine Mapping of qGL-6

Background Grain size affects not only rice yield but is also an important element in quality of appearance. However, the mechanism for inheritance of grain size is unclear. Results A rice chromosome segment substitution line Z1392, which harbors three substitution segments and produces grains of increased length, was identified. The three chromosome segments were located on chromosomes 1, 5, and 6, and the average length of the substitution segment was 3.17 Mb. Cytological analysis indicates that the predominant cause of increased grain length in Z1392 could be cell expansion in the glumes. Seven quantitative trait loci (QTLs) for grain size related traits were identified using the secondary F2 population produced by Nipponbare/Z1392. The inheritance of grain length in Z1392 was mainly controlled by two major QTLs, qGL-5 and qGL-6. qGL-6 was localized on a 1.26 Mb region on chromosome 6, and OsARF19 may be its candidate gene. Based on QTL mapping, three single-segment substitution lines (S1, S2, and S3) and two double-segment substitution lines (D1 and D2) were selected, and the mapping accuracy for qGL-5 and qGL-6 was further verified using three single-segment substitution lines. Analysis of QTL additive and epistatic effects revealed that the additive effect of alleles qGL-5 and qGL-6 from ‘Xihui 18’ was estimated to increase grain length of Z1392 by 0.22 and 0.15 mm, respectively. In addition, a positive epistatic interaction between qGL-5 and qGL-6 was detected, which indicates that the pyramiding of qGL-5 and qGL-6 for grain length produces a novel genotype with longer grains. Conclusions Inheritance of grain length in the triple-segment substitution line Z1392 is mainly controlled by two major QTLs, qGL-5 and qGL-6. qGL-6 was found to be located in a 1.26 Mb region on chromosome 6, and OsARF19 may be its candidate gene. A positive epistatic interaction between qGL-5 and qGL-6 results in longer grains. The present results can be used to facilitate cloning of the qGL-5 and qGL-6 genes and contribute to improvement of grain yield in rice.

Analysis of QTL for Grain size in a Rice Chromosome Segment Substitution Line Z1392 with Long Grains and Fine Mapping of qGL-6

Background: Grain size affects not only rice yield but is also an important element in quality of appearance. However, the mechanism for inheritance of grain size is unclear. Results: A rice chromosome segment substitution line Z1392, which harbors three substitution segments and produces grains of increased length, was identified. The three chromosome segments were located on chromosomes 1, 5, and 6, and the average length of the substitution segment was 3.17 Mb. Cytological analysis indicates that the predominant cause of increased grain length in Z1392 could be cell expansion in the glumes. Seven quantitative trait loci (QTLs) for grain size related traits were identified using the secondary F2 population produced by Nipponbare/Z1392. The inheritance of grain length in Z1392 was mainly controlled by two major QTLs, qGL-5 and qGL-6. qGL-6 was localized on a 1.26 Mb region on chromosome 6, and OsARF19 may be its candidate gene. Based on QTL mapping, three single-segment substitution lines (S1, S2, and S3) and two double-segment substitution lines (D1 and D2) were selected, and the mapping accuracy for qGL-5 and qGL-6 was further verified using three single-segment substitution lines. Analysis of QTL additive and epistatic effects revealed that the additive effect of alleles qGL-5 and qGL-6 from ‘Xihui 18’ was estimated to increase grain length of Z1392 by 0.22 and 0.15 mm, respectively. In addition, a positive epistatic interaction between qGL-5 and qGL-6 was detected, which indicates that the pyramiding of qGL-5 and qGL-6 for grain length produces a novel genotype with longer grains. Conclusions: Inheritance of grain length in the triple-segment substitution line Z1392 is mainly controlled by two major QTLs, qGL-5 and qGL-6. qGL-6 was found to be located in a 1.26 Mb region on chromosome 6, and OsARF19 may be its candidate gene. A positive epistatic interaction between qGL-5 and qGL-6 results in longer grains. The present results can be used to facilitate cloning of the qGL-5 and qGL-6 genes and contribute to improvement of grain yield in rice.