ObjectiveHeterophylly is the phenomenon that plants form multiple types of mature leaves on the same plant to adapt to the environment. Populus euphratica is a typical woody heterophyllous plant, and previous research found that there were differences between heteromorphic leaves of P. euphratica in physiological characteristics and enironmental adaption. In this study, to reveal the molecular regulation of morphological and physiological characteristics in heteromorphic leaves of P. euphratica, we analyzed the differential expression of miRNAs and functions of target genes in heteromorphic leaves of P. euphratica.

MethodIn this paper, using high-throughput sequencing, comparative study for miRNA expression patterns and functions of target genes was conducted in lanceolate leaves and dentate broad-ovate leaves.

ResultTotal of 6 high-quality sRNA libraries were obtained, and the valid sequence of each library accounted for 56%−81% of the raw data. Total 517 known miRNAs and 127 predicted novel miRNAs were identified, the length of which was mainly distributed in 20−22 nt. Besides, 389 of the identified miRNAs were mapped to 54 known miRNA families, and there were 369 miRNAs detected in both two types of leaves. Compared with lanceolate leaves, 7 miRNAs were up-regulated and in dentate broad-ovate leaves, while 15 miRNAs were down-regulated. Based on the prediction of target genes and function annotation, differentially expressed miRNAs were involved in stress-resistant pathways in Populus euphratica, such as cellular response to salt stress, inositol phosphate metabolism, cutin, suberine and wax biosynthesis, base excision repair, and RNA degradation pathways. Moreover, expression levels of 5 differentially expressed miRNAs and their corresponding target genes were examined by quantitative real-time PCR, which could confirm the expression profile of the sRNA-sequencing and the negative regulation of miRNAs on their target genes.

ConclusionOur study reveales that the expression patterns of miRNA between the heteromorphic leaves of P. euphratica are different. The miR167 and miR166 involved in growth and development of plant and miR172 associated with stress resistance of plant are up-regulated in dentate broad-ovate leaves. Besides, the miR169 and miR396 involved in stress resistance of plant are down-regulated in dentate broad-ovate leaves in comparison to lanceolate leaves. We speculate that the differential expression of miRNA may induce the morphological difference between heteromorphic leaves, and could increase the resistance of dentate broad-ovate leaves to adverse environments, this is consistent with our previous results of morphological and physiological characteristics in heteromorphic leaves of P. euphratica.