Peach calico (PC), an extreme chlorosis (albinism) of peach leaves, stems and fruits, is induced by sequence variants of the chloroplast-replicating Peach latent mosaic viroid (PLMVd, genus Pelamoviroid, family Avsunviroidae) harboring a characteristic insertion of 12-14 nt that assumes a hairpin conformation. Here, we show that the primary and not the secondary structure of the inserted hairpin plays a major role in PC, a finding consistent with the hypothesis that PC could be elicited by an RNA silencing mechanism. More specifically, viroid-derived small RNAs (sRNAs) of 21-24 nt generated by the host response against invading nucleic acids, may target for cleavage cell mRNAs thereby triggering a signal cascade that may result in PC. To test this hypothesis, we performed deep sequencing (Illumina) of sRNA libraries from healthy, PC-expressing and latently-infected peach leaves. Then, by semi-quantitative RT-PCR and RNA 3' ligase-mediated rapid amplification of cDNA ends (RACE) we determined that two PLMVd-derived sRNAs, containing the PC-associated insertion and exclusively accumulating in albino tissues, which are a target for cleavage the mRNA encoding the chloroplastic heat-shock protein 90 (cHSP90). These data are the first direct evidence that a viroid may modify thr host gene expression of its natural host via RNA silencing. Moreover, since cHSP90 participates in chloroplast biogenesis and plastid-to-nucleus signal transduction in Arabidopsis, down-regulation of this protein is consistent with the chloroplast malformations previously reported in PC-expressing tissues, and strongly supports the involvement of RNA silencing in PC. Whether symptom elicitation driven by RNA silencing is a particular case or reflects a general situation in viroid pathogenesis remains to be addressed. Since our study also identified many other peach mRNAs potentially targeted by PLMVdsRNAs, RNA silencing might have an additional role in plant-viroid interplay, including viroid evolution and adaptation. (A detailed account of these results has been recently published: Navarro et al., Plant Journal 70, 991-1003, 2012).
Peach latent mosaic viroid: data supporting the involvement of RNA silencing in peach calico (extreme chlorosis)
Navarro B;Di Serio F
2012
Abstract
Peach calico (PC), an extreme chlorosis (albinism) of peach leaves, stems and fruits, is induced by sequence variants of the chloroplast-replicating Peach latent mosaic viroid (PLMVd, genus Pelamoviroid, family Avsunviroidae) harboring a characteristic insertion of 12-14 nt that assumes a hairpin conformation. Here, we show that the primary and not the secondary structure of the inserted hairpin plays a major role in PC, a finding consistent with the hypothesis that PC could be elicited by an RNA silencing mechanism. More specifically, viroid-derived small RNAs (sRNAs) of 21-24 nt generated by the host response against invading nucleic acids, may target for cleavage cell mRNAs thereby triggering a signal cascade that may result in PC. To test this hypothesis, we performed deep sequencing (Illumina) of sRNA libraries from healthy, PC-expressing and latently-infected peach leaves. Then, by semi-quantitative RT-PCR and RNA 3' ligase-mediated rapid amplification of cDNA ends (RACE) we determined that two PLMVd-derived sRNAs, containing the PC-associated insertion and exclusively accumulating in albino tissues, which are a target for cleavage the mRNA encoding the chloroplastic heat-shock protein 90 (cHSP90). These data are the first direct evidence that a viroid may modify thr host gene expression of its natural host via RNA silencing. Moreover, since cHSP90 participates in chloroplast biogenesis and plastid-to-nucleus signal transduction in Arabidopsis, down-regulation of this protein is consistent with the chloroplast malformations previously reported in PC-expressing tissues, and strongly supports the involvement of RNA silencing in PC. Whether symptom elicitation driven by RNA silencing is a particular case or reflects a general situation in viroid pathogenesis remains to be addressed. Since our study also identified many other peach mRNAs potentially targeted by PLMVdsRNAs, RNA silencing might have an additional role in plant-viroid interplay, including viroid evolution and adaptation. (A detailed account of these results has been recently published: Navarro et al., Plant Journal 70, 991-1003, 2012).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
