Response To Cadmium Stress In Rice Bud And Its Genetic Basis

As a heavy metal pollutant,cadmium(Cd)causes serious harm to the safe production of crops.Rice(Oryza sativa L.)is one of the main food crops in China and the world,with a strong absorption and accumulation of Cd,indica rice and japonica rice are two subspecies of cultivated rice,which have different tolerance to Cd.It is of great significance to explore the different response mechanisms of indica rice and japonica rice under Cd stress to explain the genetic mechanism of Cd response in rice.In this study,Cdsensitive indica rice restorer line Changhui 891(CH891)and Cd-resistant japonica rice variety 02428 were used as materials.buds of CH891 and 02428 under Cd treatment and control for 3 and 5 days were selected to be transcriptome sequenced and analyzed by RNA-Seq technology.Meanwhile,the backcross inbred lines(BILs)population constructed by CH891 and 02428 were used to locate the QTL of root length and bud length under Cd treatment.And Cd resistance of different rice varieties was studied by treating 207 rice species with Cd.The results are as follows:(1)Stress and control treatment of CH891 and 02428 were carried out with Cd solution and pure water,and the phenotypic data of the buds were recorded and analyzed for one week.It was found that the sensitivity of CH891 and 02428 to cadmium stress was different.Under the control condition,CH891 buds were significantly longer than 02428,while the length of CH891 buds under Cd treatment had no significant difference with 02428,indicating that the sensitivity of CH891 to Cd was higher than that of 02428.(2)Illumina HiSeq 4000 sequencing platform was used to sequence the transcriptome of CH891 and 02428 buds under Cd treatment and control for 3 days and 5 days.On the third and fifth days,7204 and 6670 differentially expressed genes(DEGs)were detected,respectively.On the third day,849 genes with specific expression in CH891(SCR),676 genes with specific expression in 02428(RCR),and 770 genes with different expression levels in CH891 and 02428(CCR)were detected.On the third day,a total of 849 SCR genes,676 RCR genes and 770 CCR genes were detected.On the fifth day,a total of 959 SCR genes,592 RCR genes and 1516 CCR genes were detected.We selected important Cd-responsive(ICR)genes in the three categories with |log2(fold change)|≥ 2 and FPKM≥2 in at least one group to select representative DEGs.All these DEGs mainly enriched in plant hormone signal transduction,phenylpropanoid biosynthesis,ABC transporters,brassinosteroid biosynthesis,diterpenoid biosynthesis,ribosome,regulation of autophagy,GSH metabolism,plant-pathogen interaction,isoflavone biosynthesis and anthocyanin biosynthesis pathways.The results showed that the response mechanism of rice to Cd stress was not only species-specific,but also time-specific.(3)CH891,02428 and the BILs were treated with Cd,there was great difference on bud length and root length between different lines.The variation coefficients of root length were high to 56%and 57.14%on the 3rd and 5th day under Cd stress.The variation coefficients of bud length was 32.39%on the 3rd day while 12.02%on the 5th day.Under cadmium stress,there were obvious differences among different lines and the cadmium response was complex.(4)The QTL sites of root length and the bud length of the BIL population were located three and five days after cadmium treatment by Ici QTLMapping 4.2.A total of three QTL sites were located,namely q-RL-3,q-SL-3 and q-SL-6.q-RL-3 is a root length related QTL,located on chromosome 3,with a LOD value of 4.43 and a contribution rate of 16.02%,the synergistic allele comes from 02428.q-SL-3 and q-SL-6 are shoot length related QTLs,located on chromosome 3 and chromosome 6,with LOD values of 4.32 and 2.61,with a contribution rate of 13.08%and 7.31%,the synergistic allele comes from CH891,respectively.(5)Compared ICR genes with the located QTLs of bud length under Cd stress,In the interval of q-sl-3,only one new gene LOC_Os03g03600 was expressed under cadmium stress.Bioinformatics analysis showed that LOC_Os03g03600 is predicted to encode a fasciclin-like arabinogalactan protein 2,which plays an important role in cell proliferation and growth,cell differentiation,programmed cell death,and stress response.Therefore,it was speculated that the absence of AGP2 significantly reduces the initial velocity of polyamines,thereby reducing the toxicity of rice Cd.(6)Cd was treated in natural population which contains 207 rice varieties,and the relative bud length and the relative root length of each bud were calculated.It was found that Cd stress had a general inhibitory effect on the growth of rice buds,and the effect of Cd stress on relative root length was stronger than that on relative bud length,and the longer the time,the more obvious the inhibitory effect.The results showed that the inhibition effect of Cd on the bud length of indica rice and japonica rice buds was not significant,but the inhibition effect on the root length of japonica rice buds was greater than that of indica rice.