The poly(A) site selection and the salicylic acid signaling modulate the responses to low nitrogen availability

Nitrogen (N) is an essential nutrient for plant growth and production. For plant improvement, we need to identify and understand the mechanisms that plants have evolved to cope with N deficiency. Here, we have identified novel molecular mechanisms that connect N starvation responses with alternative polyadenylation and salicylic acid signaling.

Nitrogen (N) is an essential element for plant growth and production. In many soils dedicated for agriculture, the level of N is low, and therefore, a continuous supply of fertilizers is required. This agriculture practice has generated environmental problems, such as eutrophication of groundwater and the expansion of algae that consume oxygen from the water and the degradation the environment. Understanding how plants regulate and respond to a low concentration of N in the soil has been the subject of multiple studies, being many of them focused on analyzing changes in gene expression (transcriptomic). Recent works show that alternative polyadenylation (APA) plays a relevant role in stress responses. Mechanistically, APA introduces new poly (A) tails in the messengers at different sites than conventional ones, generating new transcripts, which in turn, produces new proteins or affects the protein synthesis at different levels. In this work, we have shown that a mutant, fip1-2, which has altered the APA process, has a differential response to N deficiency compared to wild plants. A massive analysis of polyadenylation sites in response to N deficiency in control and fip1-2 plants has allowed us to identify more than 700 differentially regulated transcripts. Most of them correspond to genes related to N metabolism, stress responses and hormonal signaling. A hormone quantification has revealed that salicylic acid (SA) accumulates at high levels in response to N deprivation in both the roots and the aerial part. Through meta-genomic analyses, we have found that a significant number of genes controlled by SA or N deficiency are also transcriptional de-regulated in the mutant fip1-2 or APA-regulated in wild type or fip1-2 seedlings, indicating that the regulation by APA is connecting SA and N deficiency. This hypothesis has been corroborated by genetic and physiological analysis: (1) treatment with SA decreases the internal levels of nitrate in plants and, (2) SA-deficient mutants contained higher levels of nitrate and a greater root system. Based on these results, we have incorporated two new levels of regulation in the response to the deficiency of N; APA regulation that will amplify the transcriptomic response and the SA signaling, that possibly regulates the balance root growth/levels of N in a plant. Thus, these results will help to understand how plants face low levels of N and will allow us to design better approaches to increase plant production with less fertilizer use.

Original Paper:

Conesa, C.M., Saez, A., Navarro-Neila, S., de Lorenzo, L., Hunt, A.G., Sepúlveda, E.B., Baigorri, R., Garcia-Mina, J.M., Zamarreño, A.M., Sacristán, S., del Pozo, J.C. 2020. Alternative Polyadenylation and Salicylic Acid Modulate Root Responses to Low Nitrogen Availability. Plants 9, 251. DOI: 10.3390/plants9020251