Abstract
Plant micro RNAs (miRNAs) control growth, development and stress tolerance but are comparatively unexplored in banana, whose cultivation is threatened by abiotic stress and nutrient deficiencies. In this study, a native Musa-miR397 precursor harboring 11 copper-responsive GTAC motifs in its promoter element was identified from banana genome. Musa-miR397 was significantly upregulated (8–10) fold in banana roots and leaves under copper deficiency, correlating with expression of root copper deficiency marker genes such as Musa-COPT and Musa-FRO2. Correspondingly, target laccases were significantly downregulated (>−2 fold), indicating miRNA-mediated silencing for Cu salvaging. No significant expression changes in the miR397-laccase module were observed under iron stress. Musa-miR397 was also significantly upregulated (>2 fold) under ABA, MV and heat treatments but downregulated under NaCl stress, indicating universal stress-responsiveness. Further, Musa-miR397 overexpression in banana significantly increased plant growth by 2–3 fold compared with wild-type but did not compromise tolerance towards Cu deficiency and NaCl stress. RNA-seq of transgenic and wild type plants revealed modulation in expression of 71 genes related to diverse aspects of growth and development, collectively promoting enhanced biomass. Summing up, our results not only portray Musa-miR397 as a candidate for enhancing plant biomass but also highlight it at the crossroads of growth-defense trade-offs.
Highlights
Plant micro RNAs control growth, development and stress tolerance but are comparatively unexplored in banana, whose cultivation is threatened by abiotic stress and nutrient deficiencies
Plants have evolved a sophisticated system of Cu uptake transport and chelation, which is controlled in part by the master transcriptional factor (TF) SQUAMOSA PROMOTER BINDING-LIKE 7 (SPL7)
Our observations agree with the finding in Arabidopsis that Cu deficiency increases lateral root density without affecting primary and lateral root length, reflecting enhanced scavenging for residual copper[29]
Summary
Plant micro RNAs (miRNAs) control growth, development and stress tolerance but are comparatively unexplored in banana, whose cultivation is threatened by abiotic stress and nutrient deficiencies. Our results prove that Musa-miR397 expression is highly sensitive to mild Cu deficiency and it can target different laccases in both root and shoot. Our results suggest that though Cu deficiency response and Fe homeostasis in banana share many of the known Fe-regulated transporters, Cu regulates the Musa-miR397-laccase module, at least in the root tissue.
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