| As a basic condition for plant growth,light not only plays a decisive role in assimilate generation,but also acts as an environmental signal to regulate plant morphogenesis and cell differentiation.Before germination and breaking ground,plants show various characteristics of yellowing,such as long and thin stems,hooked curves at the top,and small yellow-white leaves.This process is called "skotomorphogenesis".After breaking the soil and seeing light,plants underwent "photomorphogenesis",which showed that hypocotyl elongation was blocked,proplastids developed into chloroplasts,and cotyledons opened.However,most of the relevant studies have focused on the above-ground morphogenesis,and there are few reports on how light signals regulate root genesis and growth.Micro RNAs(mi RNAs)play key roles in the posttranscriptional regulation of gene expression in plants.Many mi RNAs are responsive to environmental signals.Light is the first environmental signal perceived by plants after emergence from the soil.However,less is known about the roles and regulatory mechanism of mi RNAs in response to light signal.Here,using small RNA sequencing,we determined that mi R163 is significantly rapidly induced by light signaling in Arabidopsis thaliana seedlings.The lightinducible response of mi R163 functions genetically downstream of HY5,a central positive regulator of photomorphogenesis.HY5 directly binds to the two G/C-hybrid elements in the mi R163 promoter with unequal affinity;one of these elements,which is located next to the transcription start site,plays a major role in light-induced expression of mi R163.Overexpression of mi R163 rescued the defective primary root elongation of hy5 seedlings without affecting lateral root growth,whereas overexpressing of mi R163 target PXMT1 inhibited primary root elongation.These findings provide insight into understanding the post-transcriptional regulation of root photomorphogenesis mediated by the HY5-mi R163-PXMT1 network. |
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