View source for IC4R009-miRNA-2010-20729483

==Project Title==
* '''Genome-wide identification and analysis of drought-responsive microRNAs in Oryza sativa'''

==The Background of This Project==
* In addition to regulating growth and development, the most important function of microRNAs (miRNAs) in plants is the regulation of a variety of cellular processes underlying plant adaptation to environmental stresses. In this project, to gain a deep understanding of the mechanism of drought tolerance in rice, the researchers carried out genome-wide profiling and analysis of miRNAs in drought-challenged rice across a wide range of developmental stages, from tillering to inflorescence formation, using a microarray platform.

==Plant Culture & Treatment==
* Twenty pre-germinated seeds of rice cv. IRAT109 were planted in soil in a 1/5000a Wagner’s pot. Four pots of rice plants were grown in parallel; one was subject to stress treatment at the tillering stage, one was stress challenged at the inflorescenceforming stage, and the other two pots were grown under normal condition; that is, without suffering drought stress caused by withholding of water as in the treatments. At growth stage 6.1 which is characterized by the number of leaves on the main stem of a plant, that is equivalent to the tillering stage in paddy field production, water was withheld to develop drought stress, while control pots received normal watering. Typical stress symptoms, such as leaf rolling, appeared on the eighth day after water withholding (8 DAW) when the absolute water content of the soil decreased to <4.5%. Total RNA was then extracted on 10, 12, and 14 DAW using TRNzol Total RNA Reagent (Tiangen, China) according to the manufacturer’s instructions. The growth status of the stressed rice is shown in Fig. 1A. The second drought stress was then imposed when the flag leaf appeared. Stress symptoms started to emerge on 4 DAW and total RNA was extracted on 5 and 6 DAW (Fig. 1B). RNA was extracted from the plants grown in the control pots in the above two phases. These RNA samples were profiled by a miRNA array platform.

[[File:IC4R009-miRNA-2010-20729483-f1.png |center |thumb |500px |'''Figure 1. Growing status of rice plants under drought stress.''']]

==Research Findings==
*The results indicated that 16 miRNAs, namely miR156, miR159, miR168, miR170, miR171, miR172, miR319, miR396, miR397, miR408, miR529, miR896, miR1030,
miR1035, miR1050, miR1088, and miR1126, were significantly down-regulated in response to drought stress (Table 1). Conversely, 14 miRNAs, namely miR159, miR169, miR171, miR319, miR395, miR474, miR845, miR851, miR854, miR896, miR901, miR903, miR1026, and miR1125, were significantly up-regulated under drought stress conditions.

[[File:IC4R009-miRNA-2010-20729483-t1.png |center |thumb |800px |'''Table 1. Drought stress-induced miRNAsa identified by microarray analysis.''']]

* Among the 30 miRNAs identified as significantly down- or up-regulated under the drought stress, 11 down-regulated miRNAs (miR170, miR172, miR397, miR408, miR529, miR896, miR1030, miR1035, miR1050, miR1088, and miR1126) and eight up-regulated miRNAs (miR395, miR474, miR845, miR851, miR854, miR901, miR903, and miR1125) were revealed for the first time to be induced by drought stress in plants, and nine (miR156, miR168, miR170, miR171, miR172, miR319, miR396, miR397, and miR408) showed opposite expression to that observed in drought-stressed Arabidopsis. 

* The results of the search indicated that the functions of the target genes of the drought stress-induced miRNAs identified are in keeping with previous reports, including the morphological differentiation and development of shoot organs such as root, leaf, and floral organs, hormone signal responses, miRNA regulation, and abiotic stress responses. Except for the deduced and experimentally confirmed functions of target genes, most predicted targets remain unknown regarding their functions in plant growth and development (Fig. 2).

[[File:IC4R009-miRNA-2010-20729483-f2.png |center |thumb |800px |'''Figure 2. Functional classification of differentially expressed miRNAs induced by drought stress at the tillering and inflorescence-forming differentiation stages. (A) Drought-induced up-regulated miRNAs at each sampling stage. (B) Drought-induced down-regulated miRNAs at each sampling stage.''']]

* The most conserved down-regulated miRNAs were ath-miR170, the miR171 family, and ath-miR396, and the most conserved up-regulated miRNAs were ptc-miR474 and ath-miR854a.

==Labs working on this Project==
* National Key Laboratory of Crop Genetic Improvement, College of Plant Science, Huazhong Agricultural University, Wuhan 430070,
China
* Shanghai Agrobiological Gene Center, Shanghai 201106, China

==Corresponding Author==
*　lzc@sagc.org.cn；＆lijun@sagc.org.cn