Nitrogen Fertilizers Affect Microbial Hitchhiking to the Plant Roots.

The phenomenon of microbial hitchhiking, where nonmotile microbes utilize transspecies motility to navigate within their environment, has been observed. However, the underlying factors driving microbial hitchhiking remain unclear. Our study explored how nitrogen fertilizers affect microbial hitchhiking in soil through an in situ planting experiment. We established twelve treatments encompassing the presence and absence of plants, the presence and absence of a filter membrane that is used to prevent hitchhiking, and three nitrogen levels. Results showed that nitrogen influenced bacterial diversity in all soils, an effect thwarted by filter membranes. In the presence of plants, nitrogen significantly affected the bacterial mobility, Bacillus abundance, and plant biomass, but these effects vanished when filters were used. The correlation between motile Bacillus and rhizosphere bacteria was strong without filters at the proper nitrogen levels but weakened with membrane treatments. Thus, plants and nitrogen together, not nitrogen alone, alter the soil microbiome via hitchhiking.

Positive regulation of ABA signaling by MdCPK4 interacting with and phosphorylating MdPYL2/12 in Arabidopsis.

The phytohormone abscisic acid (ABA) regulates plant growth and development and stress resistance through the ABA receptor PYLs. To date, no interaction between CPK and PYL has been reported, even in Arabidopsis and rice. In this study, we found that MdCPK4 from Malus domestica (Md for short) interacts with two MdPYLs, MdPYL2/12, in the nucleus and the cytoplasm in vivo and phosphorylates the latter in vitro as well. Compared with the wild type (WT), the MdCPK4- or MdPYL2/12-overexpressing Arabidopsis lines showed more sensitivity to ABA, and therefore stronger drought resistance. The ABA-related genes (ABF1, ABF2, ABF4, RD29A and SnRK2.2) were significantly upregulated in the overexpressing (OE) lines after ABA treatment. These results indicate that MdCPK4 and MdPYL2/12 act as positive regulators in response to ABA-mediated drought resistance in apple. Our results reveal the relationship between MdCPK4 and MdPYL2/12 in ABA signaling, which will further enrich the molecular mechanism of drought resistance in plants.