Fine mapping and candidate gene analysis of qHD1b,a QTL that promotes flowering in common wild rice(Oryza rufipogon)by up-regulating Ehd1

Heading date(flowering time)determines the adaptability of cultivars to different environments.We report the fine mapping and candidate gene analysis of qHD1b,a quantitative trait locus(QTL)responsible for early flowering that was derived from common wild rice(O.rufipogon)under both short-day and longday conditions.The introgression line IL7391,which carried segments from common wild rice in a Zhonghui 8015(ZH8015)background,exhibited early heading compared to the background and was crossed with ZH8015 to generate BC_(5)F_(2:3) families for QTL analysis.This enabled the identification of two heading-date QTL,named qHD1b and qHD7,of which the first was selected for further research.High-resolution linkage analysis was performed in BC_(5)F_(4:5) and BC_(5)F_(6) populations,and the location of qHD1b was confined to a 112.7-kb interval containing 17 predicted genes.Five of these genes contained polymorphisms in the promoter or coding regions and were thus considered as candidates.Expression analysis revealed a positive association between LOC_Os01g11940 expression and early heading.This locus was annotated as OsFTL1,which encodes an ortholog of Arabidopsis Flowering Locus T and was the most likely candidate gene for qHD1b.Our study revealed that qHD1b acts as a floral activator that promotes flowering by up-regulating Ehd1,Hd3a,RFT1,OsMADS14,and OsMADS15 under both shortday and long-day conditions.Field experiments showed that qHD1b affected several yield-related agronomic traits including 1000-grain weight and grain length.qHD1b could be useful for marker-assisted selection and breeding of early-maturing cultivars.

OsCPK12 phosphorylates OsCATA and OsCATC to regulate H2O2 homeostasis and improve oxidative stress tolerance in rice

Calcium-dependent protein kinases(CPKs),the best-characterized calcium sensors in plants,regulate many aspects of plant growth and development as well as plant adaptation to biotic and abiotic stresses.However,how CPKs regulate the antioxidant defense system remains largely unknown.We previously found that impaired function of OsCPK12 leads to oxidative stress in rice,with more H2O2,lower catalase(CAT)activity,and lower yield.Here,we explored the roles of OsCPK12 in oxidative stress tolerance in rice.Our results show that OsCPK12 interacts with and phosphorylates OsCATA and OsCATC at Ser11.Knockout of either OsCATA or OsCATC leads to an oxidative stress phenotype accompanied by higher accumulation of H2O2.Overexpression of the phosphomimetic proteins OsCATAS11D and OsCATCS11D in oscpk12-cr reduced the level of H2O2 accumulation.Moreover,OsCATAS11D and OsCATCS11D showed enhanced catalase activity in vivo and in vitro.OsCPK12-overexpressing plants exhibited higher CAT activity as well as higher tolerance to oxidative stress.Ourndings demonstrate that OsCPK12 affects CAT enzyme activity by phosphorylating OsCATA and OsCATC at Ser11 to regulate H2O2 homeostasis,thereby mediating oxidative stress tolerance in rice.

Breeding strategies for increasing yield potential in super hybrid rice

Super hybrid rice breeding is a new breeding method combining semi-dwarf breeding and heterosis breeding using germplasm and gene-environment interactions.This paper reviews the breeding strategies of super hybrid rice breeding in China,focusing on the utilization of heterosis of indica and japonica subspecies,construction of ideal plant architecture and pyramiding of disease resistant genes in restorer lines.To develop super hybrid rice,considerable effort should be made to explore genes related with high yield,good quality,resistance to pests and diseases,tolerance to stresses.Molecular breeding methods in combination with crossing techniques should be adopted in super hybrid rice breeding.