Conserved Regulatory Pathways for Stock-Scion Healing Revealed by Comparative Analysis of Arabidopsis and Tomato Grafting Transcriptomes

Immunohistochemical dynamics of cell wall matrix polymers during tomato autograft healing

A large part of the production of tomato plants is grafted. Although it has recently been described that cell walls play an important role in tomato graft healing, the spatiotemporal dynamics of cell wall changes in this critical process remains largely unknown. The aim of this work was to immunolocalize changes in the major cell wall matrix components of autograft union tissues throughout the course of healing, from 1 to 20 days after grafting (DAG). Homogalacturonan was de novo synthetized and deposited in the cut edges, displaying the low methyl-esterified homogalacturonan a stronger labelling. Labelling of galactan side chains of rhamnogalacturonan increased until 8 DAG, although remarkably a set of cells at the graft union did not show labelling for this epitope. Changes in xylan immunolocalization were associated to the xylem vasculature development throughout, while those of xyloglucan revealed early synthesis at the cut edges. Arabinogalactan proteins increased up to 8 DAG and showed scion-rootstock asymmetry, with a higher extent in the scion. The combination of these changes appears to be related with the success of the autograft, specifically facilitating the adhesion phase between scion-rootstock tissues. This knowledge paves the way for improved grafting using methods that facilitate appropriate changes in the time and space dynamics of these cell wall compounds.

Grafting in plants: recent discoveries and new applications

Grafting is a traditional horticultural technique that makes use of plant wound healing mechanisms to join two different genotypes together to form one plant. In many agricultural systems, grafting with rootstocks controls the vigour of the scion and/or provides tolerance to deleterious soil conditions such as the presence of soil pests or pathogens or limited or excessive water or mineral nutrient supply. Much of our knowledge about the limits to grafting different genotypes together comes from empirical knowledge of horticulturalists. Until recently, researchers believed that grafting monocotyledonous plants was impossible, because they lack a vascular cambium, and that graft compatibility between different scion/rootstock combinations was restricted to closely related genotypes. Recent studies have overturned these ideas and open up the possibility of new research directions and applications for grafting in agriculture. The objective of this review is to describe and assess these recent advances in the field of grafting and, in particular, the molecular mechanisms underlining graft union formation and graft compatibility between different genotypes. The challenges of characterizing the different stages of graft union formation and phenotyping graft compatibility are examined.

Development of EST-based methylation specific PCR (MSP) markers in Crocus sativus

BACKGROUND

Saffron (Crocus sativus) is high valued spice crop, but due to its sterile nature, the crop is propagated exclusively through corms. Thus, the genetic base of this crop is very narrow, however, frequency of phenotypic variability is observed; and suggested the potential role of epigenetics in saffron crop growth and development.

METHODS AND RESULTS

To facilitate epigenetic studies in saffron, we developed 1525 methylation-specific PCR (MSP) markers using MethPrimer. For this purpose, we used 6767 EST sequences of saffron available on the NCBI database. We also mine CpG islands (2555) and found that 32.7% of EST sequences had CpG islands. Out of 1525 MSP markers developed during the present study, 725 covered the CpG islands and 800 were without CpG islands. PCR amplification was found successful for 82% of MSP markers. A preliminary analysis suggested that 53.7% of genomic sites were methylated and more prominent (60% methylations) in non-CpG island regions, although, more comprehensive studies are required to validate it further.

CONCLUSIONS

The epigenetic resource developed during the present study will strengthen the epigenetic studies like epiQTL mapping, epiGWAS to explore the molecular mechanisms and genomic/epigenomic regions associated with phenotype; and further may be utilized for saffron improvement programs through epibreeding.