miR168 targets Argonaute1A mediated miRNAs regulation pathways in response to potassium deficiency stress in tomato

BACKGROUND: Potassium (K(+)) is an essential ion for most plants, as it is involved in the regulation of growth and development. K(+) homeostasis in plant cells has evolved to facilitate plant adaptation to K(+)-deficiency stress. Argonaute1 (AGO1) is regulated by miR168 to modulate the small RNA regulatory pathway by RNA silencing complex (RISC) in tomatoes. However, the role of miR168-mediated regulation of AGO1 in the context of K(+) deficiency stress in tomatoes has not been elucidated yet. RESULTS: SlmiR168 and its target gene SlAGO1A were differentially expressed among low-K(+)-tolerant JZ34 and low-K(+)-sensitive JZ18 tomato plants. Transgenic tomato plants constitutively expressing pri-SlmiR168a showed stronger root system growth, better leaves development, and higher K(+) contents in roots under K(+)-deficiency stress than those of the transgenic tomato lines expressing rSlAGO1A (SlmiR168-resistant) and the wild type (WT). Deep sequencing analysis showed that 62 known microRNAs (miRNAs) were up-regulated in 35S:rSlAGO1 compared with WT tomatoes. The same miRNAs were down-regulated in 35S:SlmiR168a compared with WT plants. The integrated analysis found 12 miRNA/mRNA pairs from the 62 miRNAs, including the root growth and cytokinin (CTK)/abscisic acid (ABA) pathways. CONCLUSIONS: The regulation mediated by SlmiR168 of SlAGO1A contributes to the plant development under low-K(+) stress. Moreover, this regulation mechanism may influence downstream miRNA pathways in response to low-K(+) stress through the CTK/ABA and root growth modulation pathways.