A long non‐coding apple RNA, MSTRG.85814.11, acts as a transcriptional enhancer of SAUR32 and contributes to the Fe deficiency response

Iron (Fe) is an essential plant nutrient and its deficiency typically limits plant growth. Long non-coding (lnc) RNAs are involved in adaptive responses to nutrient stress; however, it is not known whether they function in the regulation of the canonical Fe-deficiency response. The expression of Malus domestica (apple) lncRNA MSTRG.85814 is induced by Fe deficiency, as identified by high-throughput strand-specific RNA-seq analysis of an apple homograft system. MSTRG.85814 has a complex structure, with 13 predicted RNA sequence variants, four of which are upregulated in the roots of plants experiencing Fe deficiency. We found that one MSTRG.85814 splice variant (MSTRG.85814.11) positively modulated its cis target mRNA derived from the small auxin upregulated gene SAUR32. This in turn promoted the expression of SAUR32 and caused an increase in the expression of a plasma membrane proton ATPase, AHA10. Using a pH imaging technique, a significant decrease in the apoplastic pH was observed to occur in the root tips of MSTRG.85814.11 or SAUR32-overexpressing apple plants. Thus MSTRG.85814.11 was shown to positively promote SAUR32 expression, which then activated proton extrusion involved in the Fe-deficiency response. These results reveal a mechanism by which lncRNA promotes environmental Fe-deficiency stress adaption.