Iron Deficiency Stress Related Genes In Malus Xiaojinensis Based On A RNA-seq Transcriptome Analysis

Malus xiaojinensis the first selected iron-efficient Malus rootstock resistant to chlorosis on a global scale. After iron deficiency stress, the pH value in the rhizosphere is decreased, the activity of ferric reductase is increased, iron absorption and transport is enhanced significantly.Genes closely related to iron deficiency were screened based on genes expression profile firstly. Then part of differently expressed genes was verified by qPCR. Finally, of all the significantly differently expressed genes we chose ROP as the target gene. The expression of ROPs in Malus xiaojinensis and Malus baccatawere detected after iron deficiency, NAA, NPA treatment, and Arabidopsisrop mutants were used for elucidating the relationship between ROPs and iron uptake process. All the experiments lay the foundation for clarifying the mechanism of Malus xiaojinensis’iron tolerance.Of all21,037significantly differently expressed genes,164genes participate in iron absorption, remobilization and signal transduction. MxHA2and MxFRO2were up-regulated significantly after12hours iron deficiency stress, which means iron absorption was enhanced. While MxNRAMP1and MxNASl were induced up-regualation on day6after iron deficiency stress, which indicates iron remobilization was enhanced after2days iron deficiency stress. The up-regualtion ofERSl, EBF1, EIN3, ERF105, RAP2.2in ethylene mediated signaling pathway and APX2, CAT, POX in ROS signaling pathway at12hour after iron starvation mean the two pathway were activated at that time. Repressors of auxintranscription factor ARFIAA9and IAA13were up-regualted at12hours after iron starvation, which mean auxin mediated signaling pathway is repressed, while the upregulation of TIR1, CUL1and ARF on day2after iron starvation indicated auxin signaling pathway was activated. Abscisic acid and Jasmonic acid mediated signaling pathway were not activated at12hours and2days after iron starvation. Therefore, in Malus xiaojinensisiron uptake was enhanced in the earlier period and iron remobilization was promoted in the later period of iron deficiency. Ethylene and ROS signaling pathway responded in the earlier period.In ROP researches, we firstly predicted the ROP family conserved domain in NCBI through AtROP1～11, then14ROPs were acquired after BLAST in ’Golden Delicious’ genome by using the conserved domain, and finally the ROPs were named MdROP1～14respectively. In the root of Malus xiaojinensis, MxROP4/6were induced up-regualtion at different time after iron deficiency, MxROP4/6/10/11were also induced up-regulation by NAA treatment whether in iron sufficient or deficient condition and the up-regulation of MxROP4/6after iron starvation were repressed by NPA treatment. In the root of Malus baccata, ROPs were not induced by iron deficiency, while MbROP6, MbROP8/9/10and MbROPll were induced up-regualtion by NAA treatment. In Arabidopsis, rop mutants were much smaller than wild type after iron starvation, the FCR activity of rop2/6was not increased as wild type after iron deficiency stress, and the expression of AtFRO2and AtIRTI in rop6/9were significantly lower than wild type after iron starvation, which meant AtROP6played an important role in signal transduction after iron deficiency. While MxROP4/6induced up-regulation after iron stress were homologous to AtROP6, which shows the importance of ROP6in signal transduction after iron deficiency. Meanwhile, ROP were not induced by iron starvation in Malus baccata.