Research On Auxin Response Factor ARF21 Regulate Roots Development In Maize

Nitrogen utilization efficiency was directly related with yield in maize, many factors affect the nitrogen efficiency, among the seedling root traits was close related to nitrogen uptake ability in maize.Auxin response factor（ARF） is a class of transcription factors by auxin regulation. It plays an important role in the auxin signal transduction pathway which affects the plant growth process, including cell elongation, apical dominance, senescence and regulation plant root growth and development, etc. To understand whether or not the auxin response factors ZmARFs family genes play a role in the regulation nitrate-mediated root growth, we use maize inbred lines Ye478, Wu312 and Ye478×Wu312 RIL population in this study to analyze expression pattern of the 31 ZmARFs genes in root of Ye478 and Wu312 under 0.04, 0.4, 4.0 and 10.0mM NO₃- treatment, clone family genes and identify gene function,to identify ZmARF21 being the QTL associated with the root phenotype through including the correlation between ZmARF21 gene and Ye478×Wu312 RIL group root traits. Results show,1) The expression patterns of ZmARFs genes were significantly different in different maize inbred lines under different NO₃- concentrations treatment. 22 ZmARFs genes was detected, among 21 genes induced by NO₃- treatment in Ye478, 12 genes were no-response to NO₃- in Wu312, which indicate that ZmARFs genes were more sensitive to NO₃- treatment in Ye478. 8 genes were no-response to 10 mM NO₃- in Ye478 and 7 genes were no-response to 10 mM NO₃- in Wu312 in belong to response to NO₃-genes, showed ZmARFs family genes were more sensitive to low concentration NO₃- treatment.2) The ZmARF9, ZmARF21 and ZmARF23 genes were isolated from different maize inbred lines,which were associated with the putative regulation roots growth QTL. Gene function analysis showed that ZmARF21 over-expression regulated taproot growth in transgenic Arabidopsis, and ZmARF21 function was different in two maize inbred lines, among Ye478-ZmARF21 improved roots growth under low nitrogen treatment in transgenic Arabidopsis.3) ZmARF21 sequence polymorphism analysis showed that insertion deletion variation was present in ZmARF21 in two parents inbred, based on the discrepancy sequences between wu312 and Ye478 to design molecular markers, and integrate these markers to constructed molecular marker map which is based on Ye478×Wu312 RIL group, it is determined that ZmARF21 was located at umc1006 mark region on chromosome 6, and this marker was related to maize roots growth（including crown root,lateral root and taproot）.4) ZmARF21 sequence polymorphism was analysed in Ye478×Wu312 RIL group, and obtained three genotype with A（Ye 478）, B（Wu312） and AB（Wu312 and Ye478）. Analysis showed that A, B and AB genotype associated with the root phenotype including SRN, CRN, LRN, PRL and SRL were no significant difference under NO₃- treatment. However the significance analysis of CRL showed CRL associated with three genotype were significant difference under NO₃- treatment, CRL was significantly higher under the low nitrogen treatment, indicated the discrepancy sequences affected maize CRL significantly in low nitrogen condition.5) Association analysis showed that contribution rate of three genotypes were different for CRL,yearly results indicated that contribution rate of A-type to CRL were 3.15%, 2.87% and 3.21%respectively, contribution rate of B-type to CRL were 0.45%, 0.76% and 0.53% respectively,contribution rate of AB-type to CRL were 1.15%, 1.28% and 1.07% respectively. Among contribution rate of A-type was the largest for CRL, the B-type was low and the contribution rate of AB-type being in between the two genotype. Because A-type only exists in Ye 478 with flourishing roots, and B-type only exists in Wu312 with not flourishing roots, based on these experimental results, speculate correlation existence in between the ZmARF21 gene and root phenotype.In conclusion, the ZmARF21 regulated roots growth under low nitrogen stress, and located at chromosome 6 associated which associated with root growth molecular markers. Association analysis showed that ZmARF21 was significantly correlation with CRL, speculated ZmARF21 is a QTL associated with roots traits in maize.