Genetic Analysis and Mapping of the Mutant Locus of a Dwarf and Compact Spike Mutant NAUH164 from Wheat Variety Sumai 3
|School||Nanjing Agricultural College|
|Course||Crop Genetics and Breeding|
|Keywords||Wheat Mutant Plant height Spike density Genetic Analysis Molecular Linkage Map Quantitative Trait Loci (QTL)|
A dwarf and compact spike mutant (NAUH164) was obtained from a mutant library of wheat variety Sumai3 that was treated with chemical mutagen Ethyl methane sulfonate (EMS). Compared with its wildtype, both the stem internode length and spike internode length of mutant NAUH164 were reduced, and resulting in its reduced height and compacted spike phenotype. Studying the genetic mechanism relating to plant height and grains per spike, which are important traits for genetic improvement, in NAUH164 will be critical for better utilization of this mutant, and the identification of molecular markers linked to genes controlling the mutant locus will be helpful for further cloning of genes related to plant height and spike density.It has been proved that Gibberellic Acid (GA) and plant height traits were closely related. According to the different reactions of wheat dwarfing genes to external application of GA, the dwarfing gene can be classified into the sensitive response to GA (synthetic type) or non-sensitive (response type). In seedlings, exogenous hormones and endogenous hormone test showed that NAUH164 and its widetype were sensitive to exogenous GA, but the amount of endogenous GA in NAUH164’s of the top leaves at jointing stage were significantly lower than that in the wildtype. In this study, the I2-KI staining method was used to detect the endosperm-amylase activity between mutant and its wildtype qualitatively. We found out in both materials the synthesis ofα-amylase could be induced by 1μM GA treatment, suggesting that NAUH164 and its wildtype were both sensitive to GA (synthetic).The inheritances of dwarf and spike density were analyzed using the F2 population derived from the cross (NAUH164×Sumai 3). The results indicated that the plant height was controlled by a single incompletely dominant gene and spike density was controlled by a single dominant gene in this population. Correlation analysis showed that the coefficient of Pearson between dwarf and dense spike was -0.939, and no recombinants between the two traits were found. This suggested that the two genes were closely linked or this was also might be result of pleiotropic effect.According to the amplification of 130 polymorphism molecular markers (including 115 SSR primer pairs and 15 EST-based primer pairs) in the (NAUH164xAlondra’s) F2population and using the JoinMap 4.0 software, a genetic map consisting of 30 linkage groups, which covered 21 chromosomes of wheat, was constrcted. The genetice map consisted of 112 anchored molecular markers, with a total length of 950.5cM, and the average genetic distance between two adjacent markers was 8.80cM. Chi-square tests were performed for the 112 polymorphic markers, it was found that at the 0.05 significance level in the standard,14 markers showed distorted segregation, and the distorted segregation ratio was 10.7%.According to this established molecular genetic map and the collected phenotype data of the (NAUH164xAlondra’s) F2 population, it was found that the compact spike was controlled by a single dominant gene, and the segregation ratios of compact spike to non-dense spike was consistent with 3:1 (x2=2.67<3.84). Hence, the gene for the compact spike was temporarily named as DCS1 (DWARF AND COMPACT SPIKE1). Linkage analysis found that DCS1 was located on chromosome 5DL, and linked to the distal of molecular marker Xgwm565. Two bulked pools were constructed and each consisted of 12 homozygous plants with compact spike or non-compact spkike phenotype. By screening the pools with 44 pairs of SSR primers near from Xgwm565, we found Xgdm63 and its neighbouring three markers (Xgdm116, wmc97 and wmc215) were also polymorphism between the two parents. The genetic distance Xgdm63 with DCS1 was 5.4cM.According to the established molecular linkage map and the collected phenotype data of plant height, Windows QTL Cartographer 2.5 was preformed using Composite Interval Mapping (CIM) method and 6 QTLs were detected on chromosomes 5D,4D and 2D, respectively, when the LOD threshold was set at 2.5 in the 2009 trial. The QTL on chr.5DL has the highest contribution ratio,60.42%. In the 2008 trial, the same QTL was also detected with its contribution ratio as 43.58%, suggesting that these was major QTL and stably expressed. This QTL was located to the same region as DCS1, indication that they might be closely linked or this might be a result of’pleiotropic effect’. QTLs on chr.4D and 2D were also detected in the two years, with their contribution ratio as 6.44%,6.70% in 2008, and 11.61%,5.81% in 2009. The amplification of two specific markers for the and Rht8 genes showed that the QTL on chr.4D should be the Rht-D1b from the parent Alondra’s, and QTL on chr.2D should be the Rht8 from the parent NAUH164’s. To summarize, the major QTL on chr.5DL should be a novel dwarf gene resulted from the EMS matagenesis.