Identification of Long-Distance Transmissible mRNA between Scion and Rootstock in Cucurbit Seedling Heterografts

Abstract

Grafting has been widely used to improve plant growth and tolerance in crop production, as well as for clarifying systemic mRNA signaling from donor to recipient tissues in organ-to-organ communication. In this study, we investigated graft partner interaction mechanisms of Cucumis sativus (Csa) and Cucurbita moschata (Cmo) using a large-scale endogenous mRNA transport. The results indicated that most mobile transcripts followed an allocation pathway from source to sink. Gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that mRNA mobility functions are universally common and individually specific. Identification of mRNA mobility between distant tissues in heterografts with RT-PCR (reverse transcription PCR), RT-qPCR (reverse transcriptional quantitative real time PCR), and clone sequencing were used to estimate 78.75% of selected mobile transcripts. Integration of bioinformatic analysis and RT-qPCR identification allowed us to hypothesize a scion-to-rootstock-to-scion feedback signal loop of Csa move-down and Cmo move-up mRNAs, where Csa scion move-down mRNAs were involved in carbon fixation and biosynthesis of amino acid pathways, and Cmo root received Csa move-down mRNA and then delivered the corresponding Cmo upward mRNA to scion to improve photosynthesis of cucumber scion. This formed a feedback signal loop of scion-to-rootstock-to scion to explain why pumpkin rootstock enhanced cucumber production in the industry, which was utilized for organ communication and mediates photosynthesis processes in heterograft cucurbit crops.

RNA Motifs and Modification Involve in RNA Long-Distance Transport in Plants

“…Sugars, amino acids, phytohormones, and macromolecules such as RNA, proteins are transported from source to distant sink through the vascular system, in which system macromolecules upload from companion cells (CC) to sieve tube (SE) via plasmodesmata (PD; Notaguchi and Okamoto, 2015 ). Till now, cDNA library and omics profiling have been commendably established to identify a wide range of RNA signaling various plants species, such as cucumber ( Cucumis sativus L.) ( Zhang et al, 2016 ; Liu et al, 2020 ), pumpkin ( Cucurbit maxima ) ( Omid et al, 2007 ), Nicotiana benthamiana/ tomato ( Solanum lycopersicum ) ( Xia et al, 2018 ), Arabidopsis ( Arabidopsis thaliana ) ( Thieme et al, 2015 ), and grapes ( Vitis vinifera ) ( Yang et al, 2015 ). Evidence of biological studies in vivo have indicated that the regulatory function of RNAs (non-coding RNA and mRNA) were involving plant growth, defense, biological/economic yield, and certain morphological characteristics ( Banerjee et al, 2009 ; Huang and Yu, 2009 ).…”

Rootstock–scion exchanging mRNAs participate in the pathways of amino acid and fatty acid metabolism in cucumber under early chilling stress

“…To better verify the transportability of RNA signaling molecules in Csa/Cmo heterografts and reverse-grafting Cmo/Csa heterograft combinations, we devised a strategy based on hypocotyl grafting of size-matched Csa and Cmo seedlings with one true leaf. To analyze graft-transmissible Csa and Cmo transcripts present in the recipient heterografted tissues, we used the mobile transcript-calling strategy previously reported [ 48 ]. The mobile transcripts identified in rootstock and scion samples from reciprocally grafted seedlings allowed us to trace the direction of movement into heterologous tissues and the species dependency of this chilling-induced movement.…”

“…Based on our results, we performed RT–PCR verification on the predicted mobile mRNA by using specific primers as described previously [ 48 ]. RT–PCR indicated that chilling triggered the upward mobility of CmoAOC2 / 3 and CmoHADH from Cmo root to Csa shoot, the downward mobility of CmoACSL and CmoSDC from Cmo shoot to Csa root, and the bidirectional mobility of CsaACSL mRNA.…”

Screening for Tolerance-Resistance to Root-knot nematode Meloidogyne incognita in Grafted and Ungrafted Cucurbit Rootstocks

“…However, since methyl bromide is banned, farmers are searching for alternative control methods. A potential solution is grafting melon sections onto tolerant or resistant rootstocks (Siguenza et al, 2005;Liu et al, 2020).…”

“…Grafting a susceptible scion onto a resistant rootstock can create resistance to a cultivar without prolonged screening as well as selection required to breed for resistance into a cultivar (Liu et al, 2020). Grafting melon on resistant or tolerant cucurbits rootstocks led to reduced nematode gall formation (Siguenza et al, 2005;Kokalis-Burelle & Rosskopf, 2011).…”