Ectopic DICER-LIKE1 Expression in P1/HC-Pro Arabidopsis Rescues Phenotypic Anomalies but Not Defects in MicroRNA and Silencing Pathways

Developmental Defects Mediated by the P1/HC-Pro Potyviral Silencing Suppressor Are Not Due to Misregulation of AUXIN RESPONSE FACTOR 8

“…Surprisingly, although overexpression of DCL1 did largely alleviate the developmental defects, it did not correct the P1/HC-Pro-associated defects in the miRNA pathway: Levels of miRNAs and their targets were unchanged from those seen in the parental P1/HC-Pro line (Mlotshwa et al, 2005). These data indicate that P1/ HC-Pro-mediated defects in development do not result from general impairments in miRNA biogenesis or function.…”

“…We were interested in further investigating the role of ARF8 in P1/HC-Pro-mediated developmental defects because the conclusion that up-regulation of ARF8 is responsible for the defects is in conflict with the earlier work on the effect of overexpression of DCL1 on P1/HC-Pro phenotype (Mlotshwa et al, 2005). Importantly, one of the miRNA and target pairs looked at in Mlotshwa et al (2005) was miR167 and its target, ARF8.…”

“…Moreover, the developmental phenotypes of P1/ HC-Pro-expressing plants differ from those caused by mutation of the miR167 target site in ARF8 or the redundantly acting ARF6. P1/HC-Pro-expressing plants have narrow serrated leaves, narrow sepals and petals, and short stamen filaments (Kasschau et al, 2003;Chapman et al, 2004;Mlotshwa et al, 2005). In contrast, mARF8 or mARF6 plants with mutated miR167 target sites do not have serrated leaves or narrow flower organ but do have elongated stamen filaments and swollen (indehiscent) anthers and are also female sterile due to arrested ovule integument growth (Wu et al, 2006).…”

“…It was noted early on that transgenic plants expressing P1/HCPro, the first discovered plant viral suppressor of silencing (Anandalakshmi et al, 1998;Kasschau and Carrington, 1998), exhibited pronounced developmental abnormalities (Anandalakshmi et al, 2000) in addition to being suppressed for silencing. These developmental defects were first observed in tobacco (Anandalakshmi et al, 2000;Mallory et al, 2002a) but were subsequently characterized in greater detail in Arabidopsis (Arabidopsis thaliana; Kasschau et al, 2003;Chapman et al, 2004;Mlotshwa et al, 2005). In Arabidopsis, P1/HC-Pro-mediated developmental defects include reduced size, serrated leaves, late flowering, and abnormalities in floral morphology resulting in reduced fertility.…”

“…Importantly, one of the miRNA and target pairs looked at in Mlotshwa et al (2005) was miR167 and its target, ARF8. Increased accumulation of ARF8 mRNA was unaffected by overexpression of DCL1 in P1/HC-Pro plants, even though the P1/HC-Pro developmental phenotype was largely eliminated.…”