Papaya is a perennial plant cultivated in tropical climates worldwide. Unfortunately, papaya is susceptible to biotic stresses (e.g., papaya ringspot virus) and is also affected by abiotic stresses (e.g., low temperatures occurring periodically in the subtropics). Therefore, it is important to discover the genes that can improve papaya’s resistance to biotic and abiotic stresses. Although the genome sequencing of papaya has been completed, little is known about microRNAs (miRNA) regulation in Carica papaya.

In a recent study, Prof. YU Diqiu and his team of Xishuangbanna Tropical Botanical Garden (XTBG) conducted an extensive survey of the miRNAs in leaves and flowers of papaya. They identified 75 conserved and 11 novel papaya miRNAs. The putative targets of the miRNAs were also predicted or/and validated experimentally. For most conserved miRNAs, the miRNA-target pairs were conserved across plant species. The researchers showed that papaya has evolved a variety of miRNA-target regulatory pathways. In addition to the conserved miRNA auto-regulation pathways, they also found papaya-specific AGO1 auto-regulation pathways. They also revealed that papaya miR535 directly regulated the target genes of miR156, which was analogous to the case of miR529 in rice. In contrast to the high conservation of miR156, both miR529 and miR535 were less conserved.

Their results indicated that miRNA-mediated regulation of NB-LRR existed in papaya, suggesting a conserved miRNA regulation cascade against pathogens in plants. They also uncovered that miR-c4 mediated the regulation of ethylene signaling pathways, which may represent a new expression regulation during fruit development and ripening.

Although there is still more to be learnt about the biological significance of those miRNA-mediated pathways, their identification advances the understanding of plant miRNA function and evolution.

 The study entitled “Identification of miRNAs and miRNA-mediated regulatory pathways in Carica papaya” has been published online in Planta.