Therefore, our finding of significantly reduced expression of EglMIR156.5 in juvenile leaves of E. globulus plants with precocious phase change, relative to those with normal phase change, is consistent with genetic variation affecting the miRNA regulatory network contributing to heterochronic differentiation.
Loss-of-function mutation of AtCYP40 showed a precocious phase change with reduced number of juvenile leaves, but no alteration of flowering time [ 20].
Ten plants of precocious phase change ecotype (from four open-pollinated families of the Lighthouse provenance) and nine plants of normal phase change ecotype (six plants from three open-pollinated families of Tidal River and three plants from a Taranna family related to a grandparent of the F2) were grown in a randomized design in a glasshouse under natural light.
Because the relative contribution of individual miR156 precursor loci to the mature pool of miR156 and how this varies in different taxa are not well-understood, it is quite possible that in E. globulus ecotypic variation in the expression of EglMIR156.5 alone could result in substantially reduced miRNA156 levels, and therefore precocious phase change.
The sensitivity of MRI for detecting precocious denervation changes in early stages of HMN and CMT has been also recently confirmed [45].
Quantitative trait loci analysis in an outcross F2 family derived from crosses between individuals from a coastal population of E. globulus with precocious vegetative phase change and individuals from populations in which vegetative phase change occurs several years later implicated the microRNA EglMIR156.5 as a potential contributor to this heterochronic difference.
Here, we aim to elucidate the molecular genetic basis of adaptive differentiation between E. globulus ecotypes with precocious vegetative phase change and those in which the timing of vegetative phase change is more characteristic of the species norm.
In this study we examined the molecular basis of heterochronic differentiation between naturally occurring ecotypes of the forest tree E. globulus with precocious vegetative phase change and those in which the timing of vegetative phase change is more characteristic of the species norm.
Reactions were normalized as in Hecht et al. (2011) and the t test between mean values for precocious and normal phase change phenotypes was conducted as described above.
While our expression analysis of the miR156 precursor loci was not exhaustive, the fact that EglMIR156.5 was the only locus to display differential expression between precocious and normal phase change ecotypes is consistent with the regulation of this locus alone.
