Abstract
Pecan [Carya illinoinensis (Wangenh.) K. Koch] is an economically important nut tree and grafting is often used for clonal propagation of cultivars. However, there is a lack of research on the effects of rootstocks on scions, which are meaningful targets for directed breeding of pecan grafts. MicroRNAs (miRNAs) play an important role in many biological processes, but the mechanism underlying the involvement of miRNAs in grafting-conferred physiological changes is unclear. To identify the grafting-responsive miRNAs that may be involved in the regulation of growth in grafted pecan, six small RNA libraries were constructed from the phloem of two groups of grafts with significantly different growth performance on short and tall rootstocks. A total of 441 conserved miRNAs belonging to 42 miRNA families and 603 novel miRNAs were identified. Among the identified miRNAs, 24 (seven conserved and 17 novel) were significantly differentially expressed by the different grafts, implying that they might be responsive to grafting and potentially involved in the regulation of graft growth. Ninety-five target genes were predicted for the differentially expressed miRNAs; gene annotation was available for 33 of these. Analysis of their targets suggested that the miRNAs may regulate auxin transport, cell activity, and inorganic phosphate (Pi) acquisition, and thereby, mediate pecan graft growth. Use of the recently-published pecan genome enabled identification of a substantial population of miRNAs, which are now available for further research. We also identified the grafting-responsive miRNAs and their potential roles in pecan graft growth, providing a basis for research on long-distance regulation in grafted pecan.
Highlights
As a traditional clonal propagation technique, grafting is widely used in horticultural crops.It combines materials from two different plants: the bottom part of one plant, or rootstock, which contributes roots and support; and the upper part, or scion, from another plant, contributing stems, leaves, flowers, and fruits [1]
The main objective of our study was to enrich our knowledge of the miRNA population in pecan and explore grafting-responsive miRNAs associated with different growth vigor
Gene expression patterns have been investigated in scions of different growth vigor[40]
Summary
As a traditional clonal propagation technique, grafting is widely used in horticultural crops. It combines materials from two different plants: the bottom part of one plant, or rootstock, which contributes roots and support; and the upper part, or scion, from another plant, contributing stems, leaves, flowers, and fruits [1]. Rootstock-induced differences in the growth vigor of scions have mainly been investigated in fruit trees, especially in relation to dwarfing rootstocks. The physiological mechanisms involved have attracted much attention, and research has revealed that rootstock can affect tree vigor by influencing hormonal balance [6], mineral nutrition [7], and/or water relations [8]. Some researchers have investigated the gene expression patterns in scions with varying growth vigor on different rootstocks [9,10,11], the molecular mechanisms involved are largely unknown
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