Edited by Tamas DalmayKeywords: Tomato miR156 Plant architecture Inflorescence structure Fruit development a b s t r a c t Plant microRNAs (miRNAs) are vital components of the translation control system that regulates plant development and reproduction. The biological function of sly-miR156 was investigated by over-expression in tomato plants. Transgenic tomato plants exhibited a drastically altered phenotype, with reduced height, smaller but more numerous leaves, and smaller fruit. The inflorescence structure of sly-miR156 over-expressing plants phenocopied the sft mutant. The putative targets of sly-miR156 were identified by data base search and included six SQUAMOSA PROMOTER BINDING PROTEIN (SBP)-box transcription factor genes. Their expression patterns were then determined in 35S-miR156a and wild type tomato plants. These target genes, as well as the tomato FLOWERING LOCUS T (FT) ortholog SFT, were significantly down-regulated in sly-miR156 over-expressing plants. These studies reveal novel phenotypes regulated by miR156.
Expression of artificial microRNAs (amiRNAs) in plants can target and degrade the invading viral RNA, consequently conferring virus resistance. Two amiRNAs, targeting the coding sequence shared by the 2a and 2b genes and the highly conserved 3' untranslated region (UTR) of Cucumber mosaic virus (CMV), respectively, were generated and introduced into the susceptible tomato. The transgenic tomato plants expressing amiRNAs displayed effective resistance to CMV infection and CMV mixed with non-targeted viruses, including tobacco mosaic virus and tomato yellow leaf curl virus. A series of grafting assays indicate scions originated from the transgenic tomato plant maintain stable resistance to CMV infection after grafted onto a CMV-infected rootstock. However, the grafting assay also suggests that the amiRNA-mediated resistance acts in a cell-autonomous manner and the amiRNA signal cannot be transmitted over long distances through the vascular system. Moreover, transgenic plants expressing amiRNA targeting the 2a and 2b viral genes displayed slightly more effective to repress CMV RNA accumulation than transgenic plants expressing amiRNA targeting the 3' UTR of viral genome did. Our work provides new evidence of the use of amiRNAs as an effective approach to engineer viral resistance in the tomato and possibly in other crops.
Overexpression of rice OsPGIP2 in Brassica napus results in resistance to Sclerotinia sclerotiorum by increasing activation of defense mechanisms and inhibiting fungal SsPG3 and SsPG6 proteins.
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