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| Title: Over-expression of miR172 causes loss of spikelet determinacy and floral organ abnormalities in rice ( Oryza sativa ) .
| | Author: Zhu QH Upadhyaya NM Gubler F Helliwell CA | | Journal: BMC Plant Biol Citation: V : 9 P : 149 Year: 2009 Type: In-Process | | Literature: oryza Field: abstract Doc ID: pub20017947 Accession (PMID): 20017947 | | Abstract: BACKGROUND : Regulation of gene expression by microRNAs ( miRNAs ) plays a crucial role in many developmental and physiological processes in plants . miRNAs act to repress expression of their target genes via mRNA cleavage or translational repression .
Dozens of miRNA families have been identified in rice , 21 of which are conserved between rice and Arabidopsis . miR172 is a conserved miRNA family which has been shown to regulate expression of APETALA2 ( AP2 ) -like transcription factors in Arabidopsis and maize .
The rice genome encodes five AP2-like genes predicted to be targets of miR172 .
To determine whether these rice AP2-like genes are regulated by miR172 and investigate the function of the target genes , we studied the effect of over-expressing two members of the miR172 family on rice plant development .
RESULTS : Analysis of miR172 expression showed that it is most highly expressed in late vegetative stages and developing panicles .
Analyses of expression of three miR172 targets showed that SUPERNUMERARY BRACT ( SNB ) and Os03g60430 have high expression in developing panicles .
Expression of miR172 was not inversely correlated with expression of its targets although miR172-mediated cleavage of SNB was detected by 5 rapid amplification of cDNA ends ( RACE ) .
Over-expression of miR172b in rice delayed the transition from spikelet meristem to floral meristem , and resulted in floral and seed developmental defects , including changes to the number and identity of floral organs , lower fertility and reduced seed weight .
Plants over-expressing miR172b not only phenocopied the T-DNA insertion mutant of SNB but showed additional defects in floret development not seen in the snb mutant .
However SNB expression was not reduced in the miR172b over-expression plants .
CONCLUSIONS : The phenotypes resulting from over-expression of miR172b suggests it represses SNB and at least one of the other miR172 targets , most likely Os03g60430 , indicating roles for other AP2-like genes in rice floret development . miR172 and the AP2-like genes had overlapping expression patterns in rice and their expression did not show an obvious negative correlation .
There was not a uniform decrease in the expression of the AP2-like miR172 target mRNAs in the miR172b over-expression plants .
These observations are consistent with miR172 functioning via translational repression or with expression of the AP2-like genes being regulated by a negative feedback loop .
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[ Sen. 8, subscore: 1.00 ]: Over-expression of miR172b in rice delayed the transition from spikelet meristem to floral meristem , and resulted in floral and seed developmental defects , including changes to the number and identity of floral organs , lower fertility and reduced seed weight .
[ Sen. 9, subscore: 1.00 ]: Plants over-expressing miR172b not only phenocopied the T-DNA insertion mutant of SNB but showed additional defects in floret development not seen in the snb mutant .
[ Sen. 10, subscore: 1.00 ]: However SNB expression was not reduced in the miR172b over-expression plants .
[ Sen. 11, subscore: 1.00 ]: CONCLUSIONS : The phenotypes resulting from over-expression of miR172b suggests it represses SNB and at least one of the other miR172 targets , most likely Os03g60430 , indicating roles for other AP2-like genes in rice floret development . miR172 and the AP2-like genes had overlapping expression patterns in rice and their expression did not show an obvious negative correlation .
[ Sen. 12, subscore: 1.00 ]: There was not a uniform decrease in the expression of the AP2-like miR172 target mRNAs in the miR172b over-expression plants .
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