Small Tandem Target Mimic (STTM) in Rice Helps Achieve Large-scale Functional Blockage of MicroRNAs

MicroRNA (miRNA) is one class of non-coding small RNAs that are universe in organisms and are about 21 nucleotides in length. miRNAs play an important role in regulating plant organ development, signal transduction and stress responses. Due to their small size and extensive genetic redundancy, it is difficult to study the function of miRNA through the traditional gene loss-of-function mutants.

Currently, most of the functional studies on miRNAs involve over expression of either miRNA precursor or miRNA-resistant target genes (miRNA-resistant). Whereas one miRNA usually regulates several target genes, these methods can only partially reveal the functions of miRNA. Recent target mimicry technologies, such as target MIMICs (MIMs) and short tandem target MIMICs (STTMs), have provided effective tools to block endogenous mature miRNA activity, making it technically possible to undertake large-scale genome-wide studies.

A research group, directed by Prof. ZHU Jiankang at Shanghai Center for Plant Stress Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, produces a large collection of transgenic short tandem target mimic (STTM) lines silencing 35 miRNA families in rice as a resource for functional studies and crop improvement.

Visual assessment of field-grown miRNA-silenced lines uncovers alterations in many valuable agronomic traits, including plant height, tiller number, and grain number, that remain stable for up to five generations. Their study not only discovers new roles of miRNAs, e.g. miR172 in culm development and panicle density and miR156 in root development, but also establishes miRNAs as an important target for crop improvement just like many transgenic lines showing changes in valuable agronomic traits. As proof of concept using newly gained knowledge on the miRNAs for crop improvement, they have chosen one of the miRNAs, miR398, for further study. The result shows that manipulation of miR398 can increase panicle length, grain number, and grain size in rice.

This work generates new insights into miRNA function in rice and provides a valuable resource for functional analysis of rice miRNAs, as well as for agronomic improvement that can be readily transferred to other important food crops.

The work, entitled “Short tandem target mimic rice lines uncover functions of miRNAs in regulating important agronomic traits” has been published in PNAS online on May 1, 2017.

Article website:
http://www.pnas.org/content/early/2017/04/27/1703752114.full.pdf?sid=39c39eff-cfb5-4185-b085-8fc4913faf12

Short tandem target mimic rice lines uncover important functions of miRNAs in regulating important agronomic traits.

A: Gross morphologies of WT (Left) and STTM156 (Right) plants at maturity.
Scale bar, 10 cm.
B: Hydroponically grown 7-d-old seedlings of WT (Left) and STTM156 (Right) plants.  Scale bar, 1 cm.
C: Grain length of WT and STTM159 plants. Scale bar, 1 cm.
D: Grain width ofWT and STTM159 plants. Scale bar, 1 cm.
E: Spikelets of WT and STTM160 after removing the palea and lemma. Scale bar, 1 mm.
F: Elongated internodes of WT and STTM172 plants. Scale bar, 10 cm.
G: Enlarged STTM172 internodes from F. Scale bar, 5 cm.
H: Panicle morphologies of WT and STTM398 plants. Scale bar, 5 cm.
I: Grain width of WT and STTM398 plants. Scale bar, 1 cm.
J: Grain length of WT and STTM398 plants. Scale bar, 1 cm.

Author Contact:
ZHU Jiankang, Senior Principal Investigator
Shanghai Center for Plant Stress Biology (PSC)
CAS Center for Excellence in Molecular Plant Sciences
Shanghai Institute of Plant Physiology and Ecology (SIPPE)
Chinese Academy of Science (CAS)
Phone: (86) 21-57078201
Fax: (86) 21- 57078213
Email: jkzhu@sibs.ac.cn