PbANK facilitates the long-distance movement of the PbWoxT1-PbPTB3 RNP complex by degrading deposited callose

Tracking the messengers: Emerging advances in mRNA-based plant communication

Messenger RNAs (mRNAs) are the templates for protein translation but can also act as non-cell-autonomous signaling molecules. Plants input endogenous and exogenous cues to mobile mRNAs and output them to local or systemic target cells and organs to support specific plant responses. Mobile mRNAs form ribonucleoprotein (RNP) complexes with proteins during transport. Components of these RNP complexes could interact with plasmodesmata (PDs), a major mediator of mRNA transport, to ensure mRNA mobility and transport selectivity. Based on advances in the last two to three years, this review summarizes mRNA transport mechanisms in local and systemic signaling from the perspective of RNP complex formation and PD transport. We also discuss the physiological roles of endogenous mRNA transport and the recently revealed roles of non-cell-autonomous mRNAs in inter-organism communication.

Long-distance transport of the pear HMGR1 mRNA via the phloem is associated with enhanced salt tolerance

Grafting is the main asexual propagation method for horticultural crops and can enhance their resistance to biotic or abiotic stress. Many mRNAs can be transported over long distances through the graft union, however, the function of mobile mRNAs remains poorly understood. Here, we exploited lists of candidate mobile mRNAs harboring potential 5-methylcytosine (m⁵C) modification in pear (Pyrus betulaefolia). dCAPS RT-PCR and RT-PCR were employed to demonstrate the mobility of the 3-hydroxy-3-methylglutaryl-coenzyme A reductase1 (PbHMGR1) mRNA in grafted plants of both pear and tobacco (Nicotiana tabacum). Overexpressing PbHMGR1 in tobacco plants enhanced salt tolerance during seed germination. In addition, both histochemical staining and GUS expression analysis showed that PbHMGR1 could directly respond to salt stress. Furthermore, it was found that the relative abundance of PbHMGR1 increased in heterografted scion, which avoided serious damage under salt stress. Collectively, these findings established that PbHMGR1 mRNA could act as a salt-responsive signal and move through the graft union to enhance salt tolerance of scion, which might be used as a new plant breeding technique to improve resistance of scion through a stress-tolerant rootstock.

The β-1,3-Glucanase Degrades Callose at Plasmodesmata to Facilitate the Transport of the Ribonucleoprotein Complex in Pyrus betulaefolia

Grafting is widely used to improve the stress tolerance and the fruit yield of horticultural crops. Ribonucleoprotein complexes formed by mRNAs and proteins play critical roles in the communication between scions and stocks of grafted plants. In Pyrus betulaefolia, ankyrin was identified previously to promote the long-distance movement of the ribonucleoprotein complex(PbWoxT1-PbPTB3) by facilitating callose degradation at plasmodesmata. However, the mechanism of the ankyrin-mediated callose degradation remains elusive. In this study, we discovered a β-1,3-glucanase (EC 3.2.1.39, PbPDBG) using ankyrin as a bait from plasmodesmata by co-immunoprecipitation and mass spectrometry. Ankyrin was required for the plasmodesmata-localization of PbPDBG. The grafting and bombardment experiments indicated that overexpressing PbPDBG resulted in decreased callose content at plasmodesmata, and thereby promoting the long-distance transport of the ribonucleoprotein complex. Altogether, our findings revealed that PbPDBG was the key factor in ankyrin-mediated callose degradation at plasmodesmata.