Under the assumption that candidate genes for Pl ARG are constitutively expressed at a weak level in non-inoculated plants [ 14, 15], seedlings were grown in the greenhouse at a 14 h light (18°C /10 h dark (16°C) cycle for eight days.
However, in contrast to typical protein-coding genes, they tend to contain few introns, are expressed at low levels, exhibit weak sequence constraints, and show limited phylogenetic conservation (Cabili et al., 2011; Derrien et al., 2012; Kutter et al., 2012; Necsulea et al., 2014).
The reverse is also observed, "weak mRNA" expressed at high levels associated to low levels of encoded proteins.
Moreover, one of the recovered isolates (CONV-R 10m-2) expressed weak levels of Lex (data not shown).
Only one PET expressed weak levels of cytoplasmic CA9 without any clinical symptoms of VHL disease in our series.
In addition, our qRT-PCR analysis (Additional file 3) suggests that most of the transcription-factor genes are expressed at low levels, which would produce weak GFP signals in promoter:GFP analyses.
Non transfected wt EL4 T cells, even upon activation, express only weak levels of cell surface PrPc (unpublished observations).
A third study done in four laboratories using the same platform to analyze tumor tissue blocks, cell lines, and RNA samples found that correlation within laboratories was only slightly better than correlation between laboratories, with correlations weakest for genes expressed at low levels [ 19].
Recently evolved proteins are markedly different from widely distributed ancient proteins; they are shorter, subject to weaker selective constraints and expressed at lower levels (Albà and Castresana, 2005; Cai et al., 2009; Liu et al., 2010; Donoghue et al., 2011; Carvunis et al., 2012; Xie et al., 2012; Wissler et al., 2013; Neme and Tautz, 2014).
In addition, lncRNAs curated manually by GENCODE have canonical gene structures and histone modifications, are expressed at lower levels, appear to be subjected to weaker evolutionary constraint than coding genes and are preferentially enriched in nucleus of the cell [7].
