‘赣南早'脐橙在干旱胁迫下的生理及转录组研究

我国脐橙产区的季节性干旱对脐橙产量和品质影响较大。‘赣南早'脐橙作为一个新品种脐橙,目前在我国脐橙产区已大面积推广。为深入了解这个新品种的耐旱性,探究早熟品种‘赣南早'脐橙应对干旱胁迫的调控机制,以‘赣南早'脐橙与‘纽荷尔'脐橙（对照）为材料,测定比较不同干旱胁迫程度下二者光合作用、干旱相关生理指标等差异,并通过RNA-Seq分析比较转录水平差异及抗氧化物酶基因表达调控。结果表明：干旱胁迫下‘赣南早'脐橙净光合速率（P_n）、蒸腾速率（T_r）、气孔导度（G_s）均显著高于‘纽荷尔'脐橙;随着干旱胁迫程度增加,‘赣南早'脐橙叶片较‘纽荷尔'脐橙更舒展,‘赣南早'脐橙相对电导率和丙二醛含量显著低于‘纽荷尔'脐橙,而保护酶超氧化物歧化酶（SOD）和过氧化物歧化酶（POD）活性变化幅度更大;‘赣南早'脐橙和‘纽荷尔'脐橙叶片可溶性糖含量无显著性差异,复水后,‘纽荷尔'脐橙叶片中可溶性糖含量极显著高于‘赣南早'脐橙。转录组测序分析表明,干旱胁迫0、10、20 d时,‘赣南早'脐橙和‘纽荷尔'脐橙间DEGs数量分别为1266、683、658个。GO富集分析显示,在干旱胁迫过程中‘赣南早'脐橙差异基因主要集中在细胞蛋白修饰过程、高分子修饰作用、含磷化合物代谢过程、蛋白修饰过程等通路,而‘纽荷尔'脐橙未见明显富集。KEGG富集分析显示,除了富集于淀粉及蔗糖通路和氨基酸及核苷酸糖代谢途径,‘赣南早'脐橙其他差异基因富集途径与‘纽荷尔'脐橙基本一致。差异基因转录因子分析显示二者在ERF家族、MYB家族、NAC家族、MYB_related家族、WRKY家族、bHLH家族、HB-other家族、HSF家族、B3家族和bZIP家族均有分布,此外,‘赣南早'脐橙特异分布于GRAS家族。根据转录组分析筛选出抗氧化酶相关基因30个,其中上调表达48%,下调表达52%。本研究结果为‘赣南早'响应干旱胁迫的生理变化提供理论依据,并为其抗旱性研究提供分子基础。

Physiological and Transcriptome Analysis of ‘Gannan Zao' Navel Orange under Drought Stress

The seasonal drought in the navel orange producing areas in China has a great impact on the yield and quality of navel orange. ‘Gannan zao' navel orange, a new variety, is widely popularized in navel orange producing areas in China. In order to deeply understand the drought tolerance of ‘Gannan zao' and explore its regulation mechanism on drought stress, the differences of photosynthesis and drought related physiological indexes between ‘Gannan zao' and ‘Newhall' under different drought stress were measured, and the transcriptional differences and the regulation of antioxidant enzyme gene expression were compared by RNA-seq analysis. The results showed that the net photosynthetic rate (P_n), stomatal conductance (G_s) and transpiration rate (T_r) of ‘Gannan zao' were significantly higher than those of ‘Newhall' under drought stress. With the increase of drought stress, the leaves of ‘Gannan zao' were more stretched than that of ‘Newhall', and the relative conductivity and malondialdehyde content of ‘Gannan zao' were significantly lower than that of ‘Newhall', while the activities of protective enzymes superoxide dismutase and peroxide dismutase changed more. There was no significant difference in soluble sugar content between ‘Gannan zao' and ‘Newhall'. After rehydration, the soluble sugar content of ‘Newhall' was significantly higher than that of ‘Gannan zao'. Transcriptome sequencing analysis showed that the number of DEGs between ‘Gannan Zao' and ‘Newhall' was 1266, 683 and 658 respectively at 0, 10 and 20 days of drought stress. Go enrichment analysis showed that the differential genes of ‘Gannan zao' were mainly concentrated in the process of cell protein modification, protein modification, polymer modification and phosphorus compound metabolism, while ‘Newhall' was not significantly enriched. KEGG enrichment analysis showed that the differential gene concentration pathways of ‘Gannan Zao' and ‘Newhall' were basically the same, while ‘Gannan zao' was also enriched in starch and sucrose pathway and amino acid and nucleotide sugar metabolism pathway. ‘Gannan zao' was also enriched in starch and sucrose pathway and amino acid and nucleotide sugar metabolism pathway. Both transcription factors were in ERF family, MYB family, NAC family, MYB_Related family, WRKY family, bHLH family, HB-other family, HSF family, B3 family and bZIP family were distributed. In addition, ‘Gannan zao' was specifically distributed in GRAS family. According to the transcriptome molecular results, 30 antioxidant enzyme related genes were screened, of which 48% were up-regulated and 52% were down regulated. The results of this study would provide a theoretical basis for the physiological changes of gannanzao in response to drought stress, and provide a molecular basis for the study of its drought resistance.