The Mapping Of Maize Cob Flat Gene （Cf1） And The Mechanism Of Salt Stress Inhibiting The Germination Of Maize Seed Embryos

As a necessary food and feed crop for people’s lives,how to improve the yield of maize has always been a topic of concern to people.The yield of maize is regulated by both internal genes and external environment.A good external environment and strong genetic variation are both beneficial to the improvement of maize yield.Therefore,helping plants to find good genes or improving stress resistance are effective ways to increase maize yield.First,the morphological changes of the maize cobs will directly affect the maize row and the number of kernels in the row,which will then affect the maize yield.In this study,we found a cob flat mutant when we screened the mutant library plants,named it Cf1（cob flat 1）,and then carried out the following studies on this mutant:（1）After obtaining a phenotypically stable mutant of Cf1 cob abnormality.The ear,tassel,ear length,ear row and 100-grain weight of Cf1 and B73 were analyzed.The results showed that,compared with B73,the meristem at the top of the ear of Cf1 had abnormal hyperplasia,with multiple growth points,obvious dents in the center line,and the whole cob was flat and widened.Compared with B73,the number of tassel branches in Cf1 decreased by 3-4 on average.The average ear length of Cf1 was 14.02 cm,an average increase of 16%compared with 12.02 cm of B73.The average number of spike rows in Cf1 was 24,an increase of 45%compared to 16 in B73.In terms of 100-grain weight,the average weight of Cf1 decreased by4%compared with that of B73.（2）By phenotypic statistics of all plants in the F₂ generation trait segregation population,it was found that they had a trait segregation ratio of 3:1,and it was determined that the trait was controlled by a recessive single gene.（3）The degree of flattening of 379 individual plants in the F₂ generation was measured and counted.After summarizing,sorting was performed to select 30 plants with extremely flat and extremely round plants,together with Mo17 and Cf1,in groups of four to construct BSA（Bulked segregant analysis）mixed pool.Through PCR amplification-gel electrophoresis band observation,it is found that there is a tight linkage at the umc1266 molecular marker,and the physical position corresponds to the chromosome 3 bin 3.06.（4）The locating population was further expanded for fine locating.The data of each individual cob in the population was counted,and 317 individual plants with extremely flat cob were sorted and screened out of the 3321 population plants for subsequent fine locating.Based on the existing results of initial mapping,10 available SSR molecular markers were intensively screened around the bin 3.06 physical interval for fine mapping.The final target interval was limited to 1.92 Mbps in size,and 62 genes were included in the current interval.Three candidate genes,Zm00001d042778,Zm00001d042810 and Zm00001d042821,were identified by analyzing the expression patterns and expression differences of these genes.Secondly,salt stress is an urgent problem facing crop cultivation now.Nearly one-fifth of the world’s cultivated land is infested by salt.And this scale is still expanding year by year.The total area of saline-alkali land in my country has exceeded 500 million mu,and most of it is distributed in the northern region,which overlaps with the maize planting area,which seriously hinders the improvement of maize production.In this study,we conducted a corresponding study on the germination mechanism of seeds under salt stress.Seed germination is a systemic response,involving signal transmission between endosperm and embryo.Analyzing the mechanism of action between endosperm and embryo under salt stress will help to further improve maize yield in our country.The experimental results are as follows:（1）Treat whole seeds,seeds with half-endosperm removed and embryos with completely removed endosperm with different concentrations of salt solution,and observe the germination rate.It was found that the germination rate of a single embryo was consistently higher than that of the other two seeds at any salt concentration.In particular,under 200 m M Na Cl treatment,the germination rate of single embryos was 52%,the germination rate of intact seeds was 4%,and the germination rate of seeds with half of the endosperm removed was 0.This suggests that maize endosperm is necessary to respond to maize salt stress,and there may be some kind of signal between endosperm and embryo in response to external salt stress.（2）Put different proportions of embryos and whole seeds under salt stress to observe the germination rate.The study found that as the proportion of intact seeds increased,embryo germination was inhibited.In addition,the endosperm of the seeds treated with salt stress was ground and placed in a petri dish to observe the germination rate of single embryos under H₂O treatment.It was found that the germination rate of a group of embryos supplemented with endosperm meal was suppressed compared to the blank control.This suggests that the endosperm releases some water-soluble signaling molecules that trigger the embryo’s dormancy response to external salt stress.（3）The quantitative results of active substances showed that three active substances,polysaccharides,polyphenols and flavonoids,were all involved in the response to external stress.The results of relevant germination experiments showed that the germination of embryos under salt stress required more polysaccharides,and salt stress restricted the transport of polysaccharides from the endosperm to the embryo,which affected the germination of the embryo;in addition,salt stress could promote the transfer of polyphenols from the endosperm to the embryo,mediated maize seed germination;under the condition of salt treatment,maize endosperm can affect the accumulation of flavonoids in embryos to respond to salt stress and regulate maize seed germination.