Abstract:

miRNAs are small non-coding RNAs of 20–24 nt widely present in eukaryotes and play important roles in plant growth and stress adaptation. Water spinach（Ipomoea aquatica）can tolerate prolonged high temperature. However，miRNAs in water spinach have not yet been identified and their role in long-time high temperature is still unknown. In this paper，taking highly heat-resistant‘Taiguo Sancha’and poorly heat-resistant‘Liuye’as material，two high-quality sRNA pools were constructed after treatment with 42 ℃ for 15 days. The number of high-quality sequences both exceeded 17.3 Mb，and the number of 24 nt clean reads in‘Taiguo Sancha’was much higher than that of‘Liuye’. After comparison with water spinach’s transcriptome，1 363 258 and 1 629 209 sequences were obtained respectively. The two libraries shared 1 047 133（11.36%）unique reads，indicating that sRNAs varied in cultivars with different heat resistance. A total of 71 miRNAs were identified in water spinach，of which 22 were differentially expressed. The target genes were predicted by TargetFinder and a sum of 233 target genes were obtained. In addition，water spinach‘Bendi Sancha’with strong-heat-resistance and weakly heat-resistant‘Zhuye’were used as materials to study the expression levels of pre-miR160，pre-miR166，pre-miR172，pre-miR393，and pre-miR3627 that were differentially expressed after long-time high temperature treatment. The results showed that the expression of pre-miR160-2 in‘Bendi Sancha’and‘Zhuye’increased significantly，but in different levels；the expression of miR166 was decreased in‘Bendi Sancha’but increased significantly in‘Zhuye’；miR172 could be induced by high temperature，however，there was no difference in the two cultivars；the expression of miR3627 was decreased in‘Bendi Sancha’after high temperature treatment while there was no obvious change in‘Zhuye’. The difference in the expression patterns of miRNA precursors suggests that the mechanism of miRNA is different during long-term high temperature in water spinach.

Key words: Ipomoea aquatica, long-time high temperature, miR160, miR166, miR393