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

Mohamad Abu-Abied,Ron Ophir,Joseph Riov,Saar Levinkron,Inna Mordehaev,Yossi Yaniv,Einat Sadot,Mor Rubinstein,David Szwerdszarf

doi:10.1186/1471-2164-15-826

Mohamad Abu-Abied, Ron Ophir + Show 7 more

Open Access

https://doi.org/10.1186/1471-2164-15-826

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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.

Highlights

The ability to form adventitious roots (AR) is an economically important trait that is lost during the juvenile-to-mature phase change in woody plants
In mature cuttings, meristematic cells were detectable adjacent to the cambium (Figure 1F) on the day of excision, and small clusters of them were detected after 3 to 6 days (Figure 1G), almost no differentiated primordia were detected after 9 to 12 days (Figure 1H and [25,26]). These observations are in agreement with previous reports which showed cell division but no root differentiation in auxin treated mature tissues of various tree species [11,12,13]
Taken together, our data indicate that the difference in expression profiles between juvenile and mature E. grandis cuttings is mostly affected by time after excision, to a lesser extent by the developmental stage of the cuttings, and least by auxin treatment

Summary

Introduction

The ability to form adventitious roots (AR) is an economically important trait that is lost during the juvenile-to-mature phase change in woody plants. Rooting capability is one of the economically important traits that are lost during the juvenile-to-mature phase change in woody plants. AR formation is a complex process, in which roots differentiate and regenerate from non-root tissues [7,8], and is often described to occur in four steps: (i) cell dedifferentiation, (ii) cell division, (iii) development of root primordia, and (iv) root emergence. Histological analysis of woody plants induced to form AR revealed that cell division (step ii) is induced in both juvenile and mature tissues, but differentiation of root primordia (step iii) occurs efficiently in juvenile cuttings but is compromised in mature cuttings [11,12,13]. Mature cuttings have often been reported to produce callus tissue instead of root primordia

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