香蕉高亲和性钾转运蛋白(HAK)家族全基因组鉴定及表达

Whole genome-wide identification and expression analysis of the high-affinity potassium transporter gene family in bananas

高亲和性钾转运蛋白(high-affinity K^(+)transporter,HAK)在植株钾离子运输中扮演着关键角色.香蕉是喜钾植物,其果实富含钾,因此研究HAK基因的序列特性和表达模式对于香蕉钾元素吸收和利用研究具有重要意义.利用生物信息学手段对香蕉HAK基因家族进行全基因组鉴定,基于转录组数据分析MaHAKs成员在根、叶、自然成熟和乙烯催熟的不同成熟阶段果实中的表达情况,利用实时荧光定量PCR(qRT-PCR)研究部分成员在不同钾浓度营养液处理的根中的表达情况.结果显示,香蕉基因组中存在24个可分为5个亚家族、分布于10条染色体上的MaHAKs成员,它们编码的蛋白含8-14个跨膜结构,且均定位于质膜.MaHAKs启动子富含激素和逆境相关响应元件,此外还具有17种转录因子的结合位点,13个MaHAKs成员启动子区含有AP2和Dof结合位点,11个MaHAKs成员启动子区含有BBR-BPC结合位点.MaHAK8、20和22在根、叶以及不同成熟阶段果实中均高水平表达.MaHAK12在根系中的表达量最高,MaHAK19在叶和乙烯催熟的果实中表达量最高,MaHAK8在自然成熟的果实中表达量最高.乙烯处理0 d、1 d与3 d的果实中MaHAK1和MaHAK19的表达量分别约为自然成熟的11.43倍和9.52倍,16.40倍和13.86倍,9.57倍和5.70倍,而MaHAK2的表达量分别约为其57.6%、70.8%和54.1%. qRT-PCR结果显示:随着钾含量的降低,MaHAK1、2、8、12和20的相对表达量呈‘先升后降’趋势,50%钾处理下,这些基因的相对表达量均极显著上调且达到最高值,分别约为100%钾的2.59倍、7.82倍、7.55倍、5.82倍和9.88倍(P <0.01),MaHAK20在25%钾处理下也极显著上调,达100%钾的2.04倍.本研究表明,MaHAKs在香蕉果实发育和根系响应低钾胁迫等过程中发挥着重要作用.

High-affinity potassium transporters(HAK) play an important role in potassium transportation. Banana is a potassium-loving plant and its fruits are rich in potassium. Investigating the sequence characteristics and expression patterns of banana HAK genes is of great importance for research on banana potassium assimilation and utilization.Whole genome wide identification and characterization of the banana HAK gene family were performed using a series of bioinformatics methods. The expression patterns in the roots, leaves, natural ripening, and ethylenetreated fruits at different ripening stages were investigated based on the transcriptome profiling data. Moreover,the expression of some banana HAK gene family members in roots under the treatments of nutrient solutions with different K concentrations was also studied using quantitative real-time PCR(qRT-PCR). In total, 24 MaHAK members that can be further classified into five subfamilies and distributed on 10 chromosomes were identified from the banana genome. The encoded proteins contained 8–14 transmembrane structures and were all located in the plasma membrane. The promoters of Ma HAKs are rich in hormone-and stress-responsive elements and contain binding sites for 17 types of transcription factors. The promoter regions of 13 MaHAKs contained AP2 and Dof binding sites, and the promoters of 11 Ma HAKs contained BBR-BPC binding sites. Transcriptome results showed that Ma HAK8, 20, and 22 were highly expressed in the roots, leaves, and fruits at different ripening stages. Ma HAK12 had the highest expression in the roots, Ma HAK19 in the leaves and ethylene-treated fruits, and Ma HAK8 in the naturally ripening fruits. At 0, 1, and 3 d after ethylene treatment, the expression levels of Ma HAK1 and 19 in the ethylenetreated fruits were higher than those of the natural ripening fruits by 11.43 and 9.52, 16.40 and 13.86, and 9.57 and 5.70 times, respectively. However, the expression level of Ma HAK2 in the ethylene-treated fruits at 0, 1, and 3 d after ethylene treatment was only approximately 57.6, 70.8, and 54.1% of the natural ripening fruits, respectively. qRT-PCR results showed that, with the decrease of K content, the expression of Ma HAK1, 2, 8, 12, and 20 all showed a ‘risefall’ pattern. The relative expression levels all peaked at 50% K treatment and were all significantly higher than other groups, at approximately 2.59, 7.82, 7.55, 5.82, and 9.88 times those of the 100% K group, respectively(P < 0.01).The relative expression level of Ma HAK20 was extremely significantly upregulated under 25% K treatment compared to that of the 100% K, by approximately 2.04 times. The results obtained in this study indicate that MaHAKs play important roles during banana fruit ripening and in banana root responses to low potassium stress.