Tuning of Sl ARF 10A dosage by sly‐miR160a is critical for auxin‐mediated compound leaf and flower development

Summary miR160 adjusts auxin‐mediated development by post‐transcriptional regulation of the auxin response factors ARF 10 / 16 / 17 . In tomato, knockdown of miR160 (sly‐miR160) suggested that it is required for auxin‐driven leaf blade outgrowth, but whether additional developmental events are adjusted by sly‐miR160 is not clear. Here, the Sl MIR 160 genes and the genes of its Sl ARF s targets were edited by CRISPR /Cas9 resulting in the isolation of loss‐of‐function mutants. In addition, hypomorphic mutants that accumulate variable reduced levels of sly‐miR160a were isolated. We found that the loss‐of‐function mutants in Sl MIR 160a ( CR ‐slmir160a ‐6/7) produced only four wiry leaves, whereas the hypomorphic mutants developed leaves and flowers with graded developmental abnormalities. Phenotypic severity correlated with the upregulation of Sl ARF 10A . Consistent with that, double mutants in Sl MIR 160a and Sl ARF 10A restored leaf and flower development indicating that over‐accumulation of Sl ARF 10A underlay the developmental abnormalities exhibited in the CR ‐slmir160a mutants. Phenotype severity also correlated with the upregulation of the SHOOT MERISTEMLESS homolog Tomato Knotted 2 , which in turn activated the transcription of the cytokinin biosynthesis genes Sl IPT 2 and Sl IPT 4 . However, no change in Tomato Knotted 2 was detected in the absence of Sl ARF 10A , suggesting that it is upregulated due to auxin signaling suppression by Sl ARF 10A . Knockout of sly‐miR160a‐targeted Sl ARF s showed that whereas Sl ARF 10A is indispensable for leaf blade outgrowth and floral organ patterning, the functions of Sl ARF 16A and Sl ARF 17 are redundant. Taken together our results suggest that sly‐miR160a promotes blade outgrowth as well as leaf and leaflet initiation and floral organ development through the quantitative regulation of its major target Sl ARF 10A .