Identification And Analysis Of Drought And Cadmium Stress Responsive Proteins In Maize

Maize?Zea mays L.?is the staple crop with the largest growing area in China,and improving its stress tolerance is one of the most important goals in maize breeding practices.Our previous efforts on drought and cadmium tolerance in maize identified 71 members from the MAPKKK family in B73using bioinformatic approaches,and RNA-Seq showed that eight of them were differentially expressed under drought condition.According to the comparative expression analysis,one particular MAPKKK gene was up-regulated in the hybrid Zhengdan 619 and eight inbred lines upon drought treatment.The association study based on RNA-Seq substantiated that seven SNPs in this gene were significantly associated with drought tolerance,indicating that it plays a crucial role in the drought tolerance at the seedling stage of maize.Such gene,locating on Chromosome 8 and encoding a chloroplast protein,was designated as ZmMAPKKK18?GRMZM2G305066?.In addition,it was shown that J724,the female parent of Jingke 968,was an inbred line with low cadmium accumulation and thus outstanding tolerance to cadmium.The present study further identification drought and cadmium stress responsive proteins in maize,with the major achievements as follows.1.The full-length homogenized cDNA library with the capacity of 2.14×10⁶ cfu was constructed for the inbred line of B73 under severe drought condition.2.By using yeast two hybrid approach,34 ZmMAPKKK18 interacting proteins were identified from the cDNA library.3.A novel member of MAPK family?GRMZM2G162333?,encoding a protein that interacted with ZmMAPKKK18,was shown to be associated with cell wall homeostasis,suggesting a new ZmMAPKKK18 dependent cascade signal transduction pathway in the response to drought.4.Metabolic pathway and GO analysis demonstrated that ZmMAPKKK18 regulated a few specific physiological and biochemical processes,such as photosynthesis light reactions,indole acetic acid biosynthesis pathway II,purine nucleotides de novo biosynthesis,oxygenic photosynthesis and cytochrome c-dependent aerobic respiration I.5.The T₃ transgenic Arabidopsis overexpressing ZmMAPKKK18 exhibited significantly stronger drought tolerance after PEG treatment than the wild type.6.The dynamic changes of the proteome in maize seedling roots?Zea mays L.cv J724?under cadmium stress was investigated by using iTRAQ.Totally 733,307,499 and 576 differentially abundant proteins at 12,24,48 and 72 h after cadmium treatment,respectively,were identified,compared with the untreated control.7.Majority of these differentially abundant proteins were annotated in the molecular functions of ribosomal synthesis,reactive oxygen species homeostasis,cell wall organization,cellular metabolism,and carbohydrate and energy metabolism.Of these,the proteins associated with ribosomal synthesis were notably responsive to cadmium stress.8.A total of 166 up-regulated and 177 down-regulated proteins with similar expression pattern were identified from at least two time points,which were regarded as candidate regulated proteins?CRPs?.Fourteen of the CRPs exhibited a common pattern at three time points and thus were regarded as super candidate regulated proteins?SCRPs?,and the corresponding transcript levels of nine SCRPs were also investigated.These 14 SCRPs provide potential targets for the further investigation of genes controlling cadmium tolerance in maize.