Salt Stress And Proteomics Analysis Of African Rice Seedlings And Involvement Of MYB Transcription Factor(OsMybcc-1)in Germination Vigor Of Rice Seeds

Over the years,rice have become staple food for almost half of the world9s population,making it the world5s second cultivated cereal crop after maize.With the world5s population anticipated to largely increase by the year 2050 to 9.8 billion,there is therefore need for increased and sustainable food production to feed the ever,growing population.However,food production is faced with numerous challenges ranging from limited land for cultivation,drought,salinity,extreme temperatures as well as biotic stresses.Thus,crops that are able to tolerate these adverse growth conditions and maintain high yield are required.Salt stress is one of the key abiotic stresses threatening agricultural production and natural ecosystems.Plants are more susceptible to both biotic and abiotic stress during the initial stages of growth.In this study,we firstly investigated the response mechanism to salt stress in the seedlings of 28 rice samples obtained from Kenya with the aim of understanding protein dynamics during salt stress at the rice seedling stage.The main results were as follows:1.Rice seedlings were subjected to 500 mM NaCl and were classified into salt sensitive,intermediate or salt tolerant.2.A representative of the sensitive(S)and tolerant(T)group was selected and subjected to 300 mM NaCl for 0,1,and 3 days,a proteomic analysis was carried out on extracted root proteins identifying 434 and 401 total reliable proteins in the tolerant and sensitive samples respectively.One-way Anova revealed 104 and 102 significantly expressed proteins in T and S samples respectively,with 13 of them being commonly expressed in the two groups.3.Proteins in the redox,stress,signaling categories among others were identified,whose expression differed between the salt tolerant and the salt sensitive samples employed in the present study.In addition,we conducted an in-depth investigation of rice seed germination,a phenomenon controlled by both endogenous and exogenous factors,and a crucial process in ensuring the continuity of life in plants that depend on it as the exclusive mode of propagation.Effective rice seed germination is required to ensure robust and healthy seedling development.Alpha-amylase,the major form of amylase with secondary carbohydrate binding sites,is a crucial enzyme throughout the growth period and life cycle of angiosperm.In rice,alpha-amylase isozymes are critical for formation of the storage starch granule during seed maturation and motivate the stored starch to nourish the developing seedling during seed germination,which will directly affect the plant growth and field yield.Alpha-amylase(RAMY1A)is highly expressed during rice seed germination and it5s under the control of phytohormones,such as GA and ABA and is regulated by several transcription factors.Previous studies showed an increase accumulation at both RNA and protein level at 48 hours of seed germination.Therefore,we studied alpha-amylase intensely to understand its classification,structure,expression trait and expression regulation in rice and other crops.The main results are as follows:1.Among the 10-rice alpha-amylases,most were exclusively expressed in the developing seed embryo and induced in seed germination process.2.A novel transcription factor,OsMybcc-1,regulating the expression of alpha-amylase was previously screened by yeast-one-hybrid.In this study,we further explored the involvement of this transcription factor in regulation of RAMylA and its overall contribution to rice germination and growth.We screened and selected pure OsMybcc-1 mutant,and constructed overexpression and complementation transgenic rice plants of OsMybcc-1.3.Comparative study of the OsMybcc-1 wildtype,mutant,and overexpression transgenic rice plants was carried out.We noted that in addition to slowed germination,the OsMybcc-1 mutant exhibited semi-dwarfism at maturity.qRT-PCR results suggested the involvement of this transcription factor in the GA responsive pathway,4.Through qualitative and quantitative assay of alpha-amylase activity,the results showed that OsMybcc-1 transcription factor is directly involved in the expression of alpha-amylase,as mutation of the transcription factor resulted in reduced alpha-amylase activity.Also,Overexpression of OsMybcc-1 greatly enhanced seed germination at high temperature.5.We overviewed the research progress of alpha-amylase with focus on seed germination,and reflected on how in-depth work might elicidate its regulation and facilitate crop breeding as an efficient biomarker.This results thus demonstrates a direct involvement of transcription factor in enhancement of rice seed germination and growth.Therefore,this study provided crucial information regarding seed germination,and the response to abiotic stress at the seedling level.Integrated together,enhancement of seed germination via the manipulation of the transcription factors boosting the expression of genes directly involved in seed germination,and abiotic stress mitigation genes identified from the proteomic dynamic study,this transgenic rice plants if generated,could ensure a sustained food production,by providing rice plants with a high germination vigor,strong vegetative growth capable of withstanding abiotic stress with eventual high yield.