Functional characterization of MdERF113 in apple.

The AP2/ERF family is an important class of transcription factors involved in plant growth and various biological processes. One of the AP2/ERF transcription factors, RAP2.6L, participates in various stresses responses. However, the function of RAP2.6L is largely unknown in apples (Malus domestica). In this study, an apple gene homologous to Arabidopsis AtRAP2.6L, MdERF113, was analyzed by bioinformatic characterization, gene expression analysis and subcellular localization assessment. MdERF113 was highly expressed in the sarcocarp and was responsive to hormonal signals and abiotic stresses. MdERF113-overexpression apple calli were less sensitive to low temperature, drought, salinity, and abscisic acid than wild-type. Subcellular localization revealed that MdERF113 was a nuclear-localized transcription factor, and yeast experiments confirmed that MdERF113 has no autonomous activation activity. Overall, this study indicated that MdERF113 plays a role in regulating plant growth under abiotic conditions.

An apple NITRATE REDUCTASE 2 gene positively regulates nitrogen utilization and abiotic stress tolerance in Arabidopsis and apple callus.

Nitrogen (N) is an essential element that plays an important role in crop biomass accumulation and quality formation. Increased crop yield is relied on excessive application of fertilizers, which usually leads to environmental pollution and unsustainable development. Thus, identification and characterization of genes involved in promoting nitrogen use efficiency is of high priority in crop breeding. The activity of nitrate reductase (NR) plays a critical role in nitrogen metabolism. In model plant Arabidopsis, NITRATE REDUCTASE 2 (NIA2), one of the two NRs, is responsible for about 90% of the NR activity. In this study, MdNIA2 gene in apple (Malus domestica) genome was screened out and identified by using AtNIA2 as bait. Phylogenetic analysis revealed that MdNIA2 had the closest evolutionary relationship with MbNIA from Malus baccata. Ectopic expression of MdNIA2 in Arabidopsis elevated the nitrogen use efficiency and increased root hair elongation and formation, resulting in promoted plant growth. Furthermore, the overexpression of MdNIA2 improved salt and drought tolerance in transgenic Arabidopsis and improved the salt tolerance of transgenic apple callus, and MdNIA2-reagualted NO metabolism might contribute to the abiotic stress tolerance. Overall, our data indicate the critical role of MdNIA2 in regulating nitrogen utilization efficiency and abiotic stress responses.