Gene expression profiling in juvenile and mature cuttings of Eucalyptus grandis reveals the importance of microtubule remodeling during adventitious root formation

Abstract

BackgroundThe ability to form adventitious roots (AR) is an economically important trait that is lost during the juvenile-to-mature phase change in woody plants. Auxin treatment, which generally promotes rooting in juvenile cuttings, is often ineffective when applied to mature cuttings. The molecular basis for this phenomenon in Eucalyptus grandis was addressed here.ResultsA comprehensive microarray analysis was performed in order to compare gene-expression profiles in juvenile and mature cuttings of E. grandis, with or without auxin treatment on days, 0, 1, 3, 6, 9 and 12 post AR induction. Under these conditions AR primordia were formed only in auxin-treated juvenile cuttings. However, clustering the expression profiles revealed that the time after induction contributed more significantly to the differences in expression than the developmental phase of the cuttings or auxin treatment. Most detected differences which were related to the developmental phase and auxin treatment occurred on day 6, which correlated with the kinetics of AR-primordia formation. Among the functional groups of transcripts that differed between juvenile and mature cuttings was that of microtubules (MT). The expression of 42 transcripts annotated as coding for tubulin, MT-associated proteins and kinesin motor proteins was validated in the same RNA samples. The results suggest a coordinated developmental and auxin dependent regulation of several MT-related transcripts in these cuttings. To determine the relevance of MT remodeling to AR formation, MTs were subjected to subtle perturbations by trifluralin, a MT disrupting drug, applied during auxin induction. Juvenile cuttings were not affected by the treatment, but rooting of mature cuttings increased from 10 to more than 40 percent.ConclusionsThe data suggest that juvenile-specific MT remodeling is involved in AR formation in E. grandis.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-826) contains supplementary material, which is available to authorized users.

Stem Anatomy and Adventitious Root Formation in Cuttings of Angophora, Corymbia and Eucalyptus

“…The precise site of adventitious root initiation was difficult to identify in C. torelliana and E. camaldulensis cuttings but the location at, or peripheral to, the vascular cambium was consistent with the sites observed recently in E. benthamii [5], E. grandis [45] and E. grandis × E. urophylla [30] stems. Importantly, adventitious roots arose from both corner and side positions within the same stem section of auxin-treated E. camaldulensis cuttings, as demonstrated recently in cuttings from E. grandis × E. urophylla that were not treated with auxin [30].…”

“…Many untreated eucalypt shoots produce just one or two adventitious roots [16,[18][19][20]37,[44][45][46]. Optimally-treated eucalypt shoots often produce a mean of about four adventitious roots but individual shoots can produce higher root numbers [3,4,9,17,[19][20][21][22][23][24]47,48].…”

Cellular dynamics during maturation‐related decline of adventitious root formation in forest tree species

“…KATANIN activity depends upon the behavior of the microtubule‐associated proteins SPIRAL 2 (SPR2) and EB1 (Wightman et al ). SPR2 and EB1b are key components of a microtubule‐related mechanism that maintains proper polar cell expansion and optimal directional growth responses (Galva et al ), indicating a possible role of cell wall modification and cytoskeleton remodeling in the capacity to form adventitious roots in both forest tree species and Arabidopsis (Díaz‐Sala et al , Hutchison et al , Abu‐Abied et al , Abu‐Abied et al , ). Early studies had proposed that cell wall‐plasma membrane interaction and communication might also provide key structural and positional signals involved in the maturation‐related decline of adventitious root formation in Arabidopsis (Díaz‐Sala et al ).…”

Comparative transcriptional analysis provides new insights into the molecular basis of adventitious rooting recalcitrance in Eucalyptus

“…This effective technology is very suitable for this kind of study because it is possible to obtain an absolute quantification of the expression of a determined gene using minimal amounts of sample (100 ng RNA) and without further amplification [40]. Although mostly used in studies with animal or human cells, particularly in oncology studies, recent papers have demonstrated its suitability for plant research as well [51,54,55].…”