Plant microRNAs play vital roles in auxin signaling via the negative regulation of auxin response factors (ARFs). Studies have shown that targeting ofARF10/16/17by miR160 is indispensable for various aspects of development, but its functions in the model crop tomato (Solanum lycopersicum) are unknown. Here we knocked down miR160 (sly–miR160) using a short tandem target mimic (STTM160), and investigated its roles in tomato development. Northern blot analysis showed that miR160 is abundant in developing ovaries. In line with this, its down-regulation perturbed ovary patterning as indicated by the excessive elongation of the proximal ends of mutant ovaries and thinning of the placenta. Following fertilization, these morphological changes led to formation of elongated, pear-shaped fruits reminiscent of those of the tomatoovatemutant. In addition,STTM160-expressing plants displayed abnormal floral organ abscission, and produced leaves, sepals and petals with diminished blades, indicating a requirement for sly–miR160 for these auxin-mediated processes. We found that sly–miR160 depletion was always associated with the up-regulation ofSlARF10A,SlARF10BandSlARF17, of which the expression ofSlARF10Aincreased the most. Despite the sly–miR160 legitimate site ofSlARF16A, its mRNA levels did not change in response to sly–miR160 down-regulation, suggesting that it may be regulated by a mechanism other than mRNA cleavage. SlARF10A and SlARF17 were previously suggested to function as inhibiting ARFs. We propose that by adjusting the expression of a group of ARF repressors, of whichSlARF10Ais a primary target, sly–miR160 regulates auxin-mediated ovary patterning as well as floral organ abscission and lateral organ lamina outgrowth.Significance Statement
Plant miRNAs play important roles in many biological processes, but the functions of only a few have been characterized in tomato. Here we show that miR160 adjusts the expression of a group of ARF repressors, thereby regulating auxin-mediated ovary patterning as well as floral organ abscission and lateral organ lamina outgrowth.