Repression of microRNA 160 results in retarded seed integument growth and smaller final seed size in cotton

microRNA 160 (miR160), targeting auxin response factors (ARFs), plays many roles in plant development. We investigated the role of the miR160/ARF axis in regulation of cotton seed size. Suppressing miR160 activity, specifically in the seed coat, led to smaller seeds and less fiber production owing to attenuated growth of the maternal integument. Scanning electron microscopy and histology showed that expansion of cells in the integument was retarded in miR160-suppressed lines. Four GhARF genes were targeted by miR160 and were upregulated in miR160-suppressed lines, indicating that a miR160/ARF axis is present in cotton. Five genes (Ghir_A05G003740, Scaffold1878G000010, Ghir_D09G024980, Ghir_A11G010730, and Ghir_A05G041590), associated with reduced seed development were downregulated in miR160-suppressed lines. Our results suggest that the miR160/ARF axis controls maternal integument growth to influence seed size by directly or indirectly regulating seed development-associated genes.