Analysis of Rice Grain Quality-Associated Quantitative Trait Loci by Using Genetic Mapping

The main objective of this research was to identify quantitative trait loci associated with rice qualities to provide reliable information for marker-assisted selection and development of new varieties. In total, 120 doubled haploid (DH) lines developed by another culture from the F1 hybrid of a cross between “Cheongcheong”, a Tongil variety, and “Nagdong”, a japonica variety, were used. A microsatellite linkage map of 222 markers spanned 2082.4 centimorgans (cM) and covered 12 rice chromosomes with an average interval of 9.4cM between markers. Eight quantitative trait loci (QTLs) were associated with rice quality, consisting of two QTLs on chromosomes 1 and 9 for amylose content;three QTLs on chromosomes 8, 9, and 10 for protein content;and three QTLs on chromosomes 2, 3, and 6 for lipid content. PCR expression levels measured using the SSR markers RM23914 for proteins and RM6266 for lipids, and RM586 showed a higher degree of amplification. The present study should be useful for improving the nutritional quality of rice by means of marker-assisted selection.

Effects of lead(Pb)-induced oxidative stress on morphological and physio-biochemical properties of rice

In rice,high concentration of lead(Pb)can cause phyto-toxicity affecting several physiological functions.Cultivation of rice varieties that are resistant to Pb-induced oxidative stress is an important management strategy in Pb-contaminated soils.In the current study,we evaluated four different rice cultivars for their response to Pb-induced stress.Three japonica type cultivars X-Jigna,Ediget,and Furat,and one Indica type cultivar Amber 33 were grown in soil containing different Pb concentrations(0 mM,0.6 mM,and 1.2 mM).The soil was treated with 0 mM or 0.6 mM or 1.2 mM Pb solution one month prior to rice seedling transplantation.Thereafter,four-week-old rice seedlings were transplanted into the treated soil and their responses were observed until maturity.The data revealed that a highest concentration of Pb(1.2 mM)induced significant reduction in agronomic traits such as plant height,number of tillers per plant,number of panicles per plant,and number of spikelets per panicle in all the rice cultivars.However,least reduction in the agronomic traits was observed in X-Jigna,whereas the highest reduction in the agronomic traits was observed in Ediget.Antioxidant activity of catalase(CAT),peroxidase(POD),polyphenol oxidase(PPO),and superoxide dismutase(SOD),was evaluated along with the accumulation of superoxide ions(O2.-),protein,proline,chlorophyll,sucrose,glucose,and fructose contents in all the rice cultivars.A significant increase in antioxidant activity and in the accumulation of proline and sucrose contents with the least reduction in the chlorophyll and protein contents was observed in X-Jigna suggesting that X-Jigna is the most tolerant among all the rice cultivars tested against Pb-stress.On the other hand,non-significant and slightly significant increase in the antioxidant activity,less accumulation of proline and sucrose contents,and higher reduction in the chlorophyll and protein contents was observed in Ediget,which further suggest that Ediget is the most susceptible rice cultivar to Pb-stress.In addition,the other rice cultivars Furat and Amber 33,were found to be moderately tolerant to Pb-induced oxidative stress.In summary,our results suggest that tolerance to Pb-induced oxidative stress would be a result of a synergetic action of both enzymatic and non-enzymatic antioxidant systems,leading to a balanced redox status in rice.

Analysis of High-Resolution QTL Markers Associated with Rice Yields Using Data for Two Consecutive Years in Different Environmental Conditions

Previously we reported the identification of seven quantitative trait loci (QTLs) associated with the rice yield measuring five parameters including panicles per plant (PPP), spikelets per panicle (SPP), seed set percentage (SSP), 1000-grain weight (TGW) and yield in 2012. Here we report the analysis of QTLs using the same trait parameters data of the mapping population in 2013 for detecting highly conserved QTL markers. A total of 6 QTLs were identified from chromosomes 1, 7, 8, 10, 11, and 12, which were contrasted with our previous results (chromosomes 1, 2, 4, 5, 6, 8, and 11). In this comparison, three QTLs from chromosome 1, 8, and 11 were only found to be associated with the components of yield over two consecutive years indicating high sensitivity of QTL markers to the environment. Of those three QTLs, SPP-associated marker RM12285 was found to be dominantly expressed by real-time PCR (qPCR). In addition, compared to our previous report the numbers of mapping population and markers were significantly increased for higher resolution markers from 70 to 120, and from 143 to 217, respectively. We also found that the parameter SPP was dominantly correlated with the rice yield. Furthermore, the double haploid (DH) population facilitated to analyze the epistatic effects for yield and yield components in rice. Taken together, combining multiple mapping population data over years possibly enables narrowing down to the highly conserved QTL markers against diverse environmental fluctuation caused by such as drought and high temperature. Thus, these data would be critically exploited to improve for the crop breeding strategy.

Immune Sensor Xa21 Regulates Bacterial Leaf Blight Infection in Seven Rice Cultivars from Myanmar

Bacterial leaf blight(BLB)is a devastating disease of rice with the potential to reduce yield by up to 70%.In this study,we investigated the genetic foundation of Xa21-mediated resistance to BLB infection in seven different rice varieties from Myanmar.The varieties exhibited a variable phenotypic response at 14 d after infection(DAI)by Xoo strains K1 and K3a,among which,the variety Kayin Ma was classified as a moderately resistant(MR)variety,expressing Xa2,Xa4,xa5,xa13,and Xa21 genes.

Redox sensor QSOX1 regulates plant immunity by targeting GSNOR to modulate ROS generation

Reactive oxygen signaling regulates numerous biological processes,including stress responses in plants.Redox sensors transduce reactive oxygen signals into cellular responses.Here,we present biochemical evidence that a plant quiescin sulfhydryl oxidase homolog(QSOX1)is a redox sensor that negatively regulates plant immunity against a bacterial pathogen.The expression level of QSOX1 is inversely correlated with pathogen-induced reactive oxygen species(ROS)accumulation.Interestingly,QSOX1 both senses and regulates ROS levels by interactingn with and mediating redox regulation of S-nitrosoglutathione reductase,which,consistent with previous findings,influences reactive nitrogen-mediated regulation of ROS generation.Collectively,our data indicate that QSOX1 is a redox sensorthat negatively regulates plant immunity by linking reactive oxygen and reactive nitrogen signaling to limit ROS production.