不同氮水平下玉米苗期根系形态和氮吸收量的QTL定位

Mapping of QTLs for root morphology and nitrogen uptake of maize under different nitrogen conditions

【目的】玉米的根系形态与氮素吸收能力关系密切,利用单片段代换群体对玉米苗期根系形态相关性状和植株氮吸收量进行QTL定位,可为进一步精细定位并克隆控制玉米低氮下优异根系形态和氮吸收的主效QTL奠定基础。【方法】以氮效率差异显著的两亲本许178和综3构建的150个玉米单片段代换系(SSSL)群体作为研究材料,进行水培试验。以Ca(NO3)2作为氮源,设置高氮(4 mmol/L NO3–)和低氮(0.05 mmol/L NO3–)两个处理,培养20 d后分根、冠收获植株,测定生物量和氮含量。通过Win RHIZO根系分析系统获得根系的总根长、根表面积、根体积、根直径和根尖数等指标。根据代换系与亲本许178表型值的T-test结果,利用该群体SSR遗传连锁图谱,在P≤0.001条件下定位所调查性状的QTL。【结果】高氮条件下SSSL群体除了根直径与总根长和根尖数没有显著相关性以外,其它各性状之间均显著或极显著正相关,并且植株氮吸收量也与根系各性状呈显著或极显著正相关;低氮条件下,除了根直径以外,植株氮吸收量与其他根系性状均呈极显著正相关,并且地上部和根部氮累积量均与根表面积的相关性最大。在高氮条件下共检测到102个QTL位点,包括40个根形态相关QTL、34个植株生物量QTL和28个氮吸收量QTL;在低氮条件下共检测到85个QTL位点,包括47个根形态QTL、22个植株生物量QTL和16个氮吸收量QTL。所检测到的根形态相关QTL与生物量和氮积累量QTL成簇存在,同一QTL区间多同时检测到根形态QTL和氮吸收量QTL。高氮条件下,在代换系1428、1376、1282、1266和1473的代换区间上检测到高氮特异的QTL簇,同时包括多个根形态和氮吸收量QTL,贡献率从–43%到84%。低氮下,在代换系1419和1314的代换区间上同时检测到低氮特异的多个根形态和氮吸收量QTL,贡献率从–32%到55%。【结论】单片段代换系1419和1314所包含的代换片段bnlg182—bnlg2295和umc1013—umc2047检测到多个低氮特异的QTL,并且这两个区间在前人的研究中均有玉米氮效率相关QTL检测到,说明该区间包含有玉米根系形态和氮吸收量的主效QTL,在玉米氮高效吸收中可能起重要作用。

[ Objectives ] There is a strong relationship between maize root morphology and nitrogen uptake capacity. In this study, QTLs for maize root morphology and plant nitrogen uptake were identified using single segment substitution lines （SSSLs） to provide support for fine mapping and cloning of major QTLs controlling maize root morphology and nitrogen uptake. [ Methods ] 150 maize SSSLs derived from a cross between a N-efficient inbred line Xu178 and a N-inefficient inbred line Zong 3 were used for solution culture. Ca（NO3）2 was used as nitrogen source and high nitrogen level （4 mmol/L NO3-） and low nitrogen level （0.05 mmol/L NOr） were supplied for each line, and each N level had six seedlings. After 20 days culture, seedlings were harvested, and the biomass and nitrogen contents of shoots and roots were analyzed respectively. Total root length （TRL）, root surface area （RSA）, root volume （RV）, root average diameter （RAD） and root tip numbers （RTN） were determined from the root images using WinRHIZO. According to the results of the T-test of the phenotype values of SSSL and Xu 178, QTLs for each trait were mapped in the S SR genetic linkage map when P value was less than 0.001. [ Results ] Under the high N level, all root traits were significantly correlated with each other except that between RAD and either TRL or RTN, and the plant nitrogen uptake was significantly correlated with all the root morphology related traits. Under the low N level, all the root morphology traits were strongly correlated with plant nitrogen uptake except for RAD, and the RSA showed the most significant correlation. Under the high N level, 102 QTLs were detected including 40 QTLs for root morphology traits, 34 QTLs for plant biomass and 28 QTLs for plant nitrogen uptake. Under the low N level, 85 QTLs were detected including 47 QTLs for root morphology traits, 22 QTLs for plant biomass and 16 QTLs for plant nitrogen uptake. Most of the QTLs for N uptake coincided in cluster with those for root morphology. Several QTLs for root morphology and nitrogen uptake were mapped in the same substituted segment region. Under the high N condition, five high N-specific QTLs clusters containing several root morphology traits and nitrogen uptake were detected in SSSL lines of 1428, 1376, 1282, 1266 and 1473. The single QTL additive effect contribution was from 43% to 84%. Moreover, several QTLs for root morphology and nitrogen uptake were identified in the SSSL lines of 1419 and 1314 under the LN condition, with the additive effect contribution from -32% to 55%. [ Conclusions ] In the present study, several LN-specific QTLs were mapped in substituted segment of bnlg 182-bnlg2295 in line 1419 and umc 1013-umc2047 in line 1314, in which some QTLs related to nitrogen use efficiency of maize were detected in previous researches. It was indicated that there were some major QTLs for maize root morphology and plant nitrogen uptake located in the two regions which would play important role in maize nitrogen uptake efficiency. The present research serves as a basis for the major QTLs fine-mapping and candidate genes cloning.