Comparative analysis of the carrot miRNAome in response to salt stress.

Soil salinity adversely affects the yield and quality of crops, including carrot. During salt stress, plant growth and development are impaired by restricted water uptake and ion cytotoxicity, leading to nutrient imbalance and oxidative burst. However, the molecular mechanisms of the carrot plant response to salt stress remain unclear. The occurrence and expression of miRNAs that are potentially involved in the regulation of carrot tolerance to salinity stress were investigated. The results of small RNA sequencing revealed that salt-sensitive (DH1) and salt-tolerant (DLBA) carrot varieties had different miRNA expression profiles. A total of 95 miRNAs were identified, including 71 novel miRNAs, of which 30 and 23 were unique to DH1 and DLBA, respectively. The comparison of NGS and qPCR results allowed identification of two conserved and five novel miRNA involved in carrot response to salt stress, and which differentiated the salt-tolerant and salt-sensitive varieties. Degradome analysis supported by in silico-based predictions and followed by expression analysis of exemplary target genes pointed at genes related to proline, glutathione, and glutamate metabolism pathways as potential miRNA targets involved in salt tolerance, and indicated that the regulation of osmoprotection and antioxidant protection, earlier identified as being more efficient in the tolerant variety, may be controlled by miRNAs. Furthermore, potential miRNA target genes involved in chloroplast protection, signal transduction and the synthesis and modification of cell wall components were indicated in plants growing in saline soil.

Antioxidative and osmoprotecting mechanisms in carrot plants tolerant to soil salinity.

Soil salinization is a growing problem for agriculture worldwide and carrot is one the most salt-sensitive vegetable species. However, some varieties are capable of withstanding high salt concentrations due to unknown genetic and physiological mechanisms. The aim of this work was to reveal protecting mechanisms against osmotic and ionic stresses that contribute to salt tolerance in carrot. For this purpose, changes in biochemical traits due to soil salinity occurring in the salt-tolerant and salt-sensitive plants were determined. The obtained results showed that the tolerance of the salt-tolerant variety was partially determined constitutively, however, the exposition to saline soil triggered a physiological response that was more evident in the root than in the leaves. The most noticeable changes were the high increase in the content of osmoprotective proline and other low molecular antioxidants such as glutathione and ascorbic acid, and the decrease in the ratio of reduced to oxidized glutathione forms. These changes imply an efficient operation of the ascorbate-glutathione cycle that together with a high activity of antioxidative enzymes such as peroxidases, indicate on the induction of mechanisms associated mainly with protection against excessive reactive oxygen species.