| Food problems have existed since ancient times and will continue to exist.Especially in the face of the outbreak of COVID-19 in 2020,China has spared no effort in promoting grain storage and land,grain storage and technology,and the "bottle neck" of provenance technology.With the continuous improvement of living standards,"rice quality" gradually appeared in the public’s vision,and people’s requirements for quality also Corresponding rise.In recent years,many studies have found that there are significant differences in grain quality in different parts of the same panicle.Of course,the author also reached a similar conclusion in the analysis of rice quality.Therefore,in order to further explore the mechanism of grain quality difference at different parts of rice panicle,this study divided rice panicle into top,middle and Bottom Spikelets.Starting with the phenotype of rice quality such as amylose and chalkiness,the analysis of physiological indicators such as hormone,free sugar,starch and related enzyme activity,and the verification of Transcriptome and Proteome,the specific differences of different grains were systematically analyzed.The results showed that:1.The thousand-grain weights of the grains from different panicle parts increased steadily during the filling stages of 0-35 days with the upper parts heaviest and the lower parts lightest.The variation coefficient of grain biomass in different panicle parts ranged from 0.017 to 0.103 on the 35 th day.After 35 d,the gaps among different panicle parts were narrowed,but the differences could be still observed.After maturity,the order of thousand-grain weight of the seeds remained as the upper(25.08-33.88g)> the middle(24.04-32.49g)> the lower(23.46-31.78g).There was a slight difference in head rice yield and length-width ratio among different panicle parts.The correlation analysis among all the parameters showed that thousand-grain weight was positively correlated with length-width ratio(r = 0.89,P< 0.01),and negatively correlated with head rice yield(r =-0.68,P< 0.01).2.The results showed that amylose content and chalkiness were the key indexes of quality difference.The amylose content of the five varieties was in an order as top>middle>bottom except xiushui 134.The chalkiness degree of jia 58 and zhongjia 8was higher than the other varieties,and the chalkiness degree of rice grains on the middle part of panicles was lower than that on the bottom part,and the rice grains on the top part had the highest chalkiness degree.In addition,the indexes of mace rice percentage,length-width ratio,gel consistency and alkali elimination value were also slightly different among different parts.Rice grains of high chalkiness degree had significant difference in starch granules size and shape.It was found that the shape of starch granules was semi-ellipsoid or other spherical curved in rice grains with high chalkiness degree and mostly regular polyhedra in rice grains with low chalkiness degree.3.Significant differences were observed among three endogenous phytohormones from three different panicle parts.The variation coefficients of SA,ABA and IAA from different panicle parts were 0.006～0.259,0.014～0.662 and 0.002～0.810,respectively.At the early stage of filling,the order of SA content presented as upper > middle > lower.At the late stage of grouting,the order of SA content presented as lower > middle > upper.4.Further experiments were carried out on jia 58,which had the largest difference in amylose,chalkiness and other key qualities in different parts of panicle.The contents of sucrose,glucose and fructose in grains of different varieties and parts were different during grain filling period,but the dynamic changes of sucrose content were firstly decreased and then slightly increased,while glucose and fructose were basically increased first and then decreased.The contents of invertase and AGPase were significantly different among rice grains on top,middle and bottom parts of panicles.However,the expression levels of AGPase was in an order as top >middle> bottom during the whole filling stage.The expression levels of invertase was in an order as top<middle< bottom during the early filling stage,and the rule was completely the opposite at late filling stage.The expression levels of Os CIN2,Os CIN5 which encoding sucrose invertase genes were in an order as middle > bottom > top,and the expression levels of Os AGPL1,Os AGPL2 and Os AGPS1 a which encoding AGPase genes were in an order as top > middle ≈ bottom.It concluded that the amylose content and chalkiness degree of grains in different panicles had significant difference and also affected by varieties.The content of soluble carbohydrate,starch biosynthesis related enzyme activity and the gene expression of encoding related enzymes had an effect on starch biosynthesis.The genes of Os CIN2,Os CIN5,Os AGPL1,Os AGPL2 and Os AGPS1 a played an important role in the difference of starch content and chalkiness degree in different panicles.5.RNA-seq showed that a total of 3567 and 12053 genes were found at one week and two weeks after full heading in different parts of paniculus of jia-58,respectively.The differential genes involved in 76 different metabolic pathways such as glucose metabolism and starch synthesis.The glucose metabolism and starch synthesis pathway which was most closely related to starch quality was one of the most varied metabolic pathways among grains from three different parts of paniculus.For glucose metabolism and starch synthesis,42 genes were found to be more than 2 times of difference in 6pairwise comparison groups.The difference of transcription levels of glucose metabolism genes in the grains from different parts of paniculus was significantly higher than that of starch synthesis genes.Combining with the GO enrichment of carbohydrate metabolism and KEGG pathway analysis of sucrose metabolism and starch synthesis,it was found that the spatio-temporal expression of Su S1(Sucrose Synthetase 1,Os03g0401300)was significant difference in the grains from different parts of paniculus.According to the expression of Su S1 and the soluble glucose content in the grains form different parts of paniculus,it can be concluded that starch quality of the grains from different parts of paniculus may be regulated by glucose and Su S1.Appropriate regulating of glucose signal or Su S1 transcription level in grains could improve the quality of grains from different parts of paniculus.In addition,transcriptomics also showed that several genes,such as Os03g0316200,Os07g0243200,Os03g0212800,Os04g0535600,Os09g0298200 and Os06g0367100,had significant differences in transcriptional levels in grains from different parts of paniculus at the early stage of grain filling.6.There was no significant difference in the number of protein in the grains from different parts of paniculus of jia 58 during the critical period of grain filling,but the difference of protein type and number gradually increased with the time of grain filling.Differential proteins were mainly concentrated in cytoplasm and nucleus,and their functions are mainly related to metabolic and cellular process.Su Sy(sucrose synthase),ADPase(ADP-glucose pyrophosphorylase)and SS(soluble starch synthase)had significant effects on sucrose metabolism and starch synthesis in the seed from different parts of paniculus.SUS4 plays a key role in sugar distribution and is closely related to sucrose content in grains from different parts of paniculus.AGPL2 protein may interact with AGPS2 to jointly affect the synthesis of ADPG in grains from different parts of paniculus.The expression levels of SS-I and SS-IIa were significantly different in grains from different parts of panicles.The effect of protein SS-I on grain filling in different parts of paniculus was significantly higher than that of protein SS-IIa and was significantly correlated with grain development level. |
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