Abstract
MicroRNAs (miRNAs) control gene expression as key negative regulators at the post-transcriptional level. MiR160 plays a pivotal role in Arabidopsis growth and development through repressing expression of its target AUXIN RESPONSE FACTOR (ARF) genes; however, the function of miR160 in monocots remains elusive. In this study, we found that the mature rice miR160 (OsmiR160) was mainly derived from OsMIR160a and OsMIR160b genes. Among four potential OsmiR160 target OsARF genes, the OsARF18 transcript was cleaved at the OsmiR160 target site. Rice transgenic plants (named mOsARF18) expressing an OsmiR160-resistant version of OsARF18 exhibited pleiotropic defects in growth and development, including dwarf stature, rolled leaves, and small seeds. mOsARF18 leaves were abnormal in bulliform cell differentiation and epidermal cell division. Starch accumulation in mOsARF18 seeds was also reduced. Moreover, auxin induced expression of OsMIR160a, OsMIR160b, and OsARF18, whereas expression of OsMIR160a and OsMIR160b as well as genes involved in auxin signaling was altered in mOsARF18 plants. Our results show that negative regulation of OsARF18 expression by OsmiR160 is critical for rice growth and development via affecting auxin signaling, which will advance future studies on the molecular mechanism by which miR160 fine-tunes auxin signaling in plants.
Highlights
OsmiR156 may target OsSPL16 to control grain size, shape, and quality[15]
Our RT-PCR results showed that expression of OsMIR160a and OsMIR160b genes was significantly higher than that of the other four OsMIR160 genes in leaf (L), young inflorescence (YI), mature inflorescence (MI), and stem (ST) (Fig. S1b)
To test whether auxin signaling was affected in mOsARF18 transgenic plants, we examined expression of representative genes known to be involved in auxin signaling in rice, including the AUXIN RESPONSIVE FACTOR gene OsARF234, the auxin responsive gene OsGH3-135, the AUX1-LIKE gene OsLAX2 (OsAUX3 or OsRAU2; Os03g14080)[36], the auxin efflux gene OsPIN1b37, and the auxin biosynthesis gene OsYUCCA238 via quantitative real-time RT-PCR (qRT-PCR)
Summary
OsmiR156 may target OsSPL16 to control grain size, shape, and quality[15]. Overexpression of OsmiR172 represses expression of AP2-like genes, which causes abnormal floral meristem identity and defects in flower organ and seed development[17,18]. Transgenic plants overexpressing OsmiR393a/b have defects similar to those observed in auxin signaling mutants[19]. Analyses using similar approaches have revealed that the miR160-controlled ARF10 is essential for seed germination and many post-embryonic growth and developmental processes through the regulation of both auxin and ABA signaling[24]. We generated transgenic rice plants (named mOsARF18) that expressed an OsmiR160-resistant version of OsARF18. Phenotypic analyses revealed that mOsARF18 plants showed pleiotropic defects in growth and development. Our results support the idea that deregulation of the OsmiR160 target gene OsARF18 leads to abnormal growth and development in rice through affecting the auxin signaling
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