Investigation of drought induced biochemical and gene expression changes in carrot cultivars.

BACKGROUND: Carrot is the most important vegetable in Apiaceae family, and it is consumed globally due to its high nutritional quality. Drought stress is major environmental constraint for vegetables especially carrot. Limited data is available regarding the mechanisms conferring drought tolerance in carrot. Methods and Results Eight commercial carrot cultivars were used in this study and subjected to drought stress under semi-controlled greenhouse conditions. Biochemical, antioxidant enzymatic activity and changes in transcript level of drought related genes was estimated, the gene expression analysis was done by using qRT-PCR in comparison with reference gene expression Actin (Act1). Results revealed that cultivars Coral Orange, Tendersweet and Solar Yellow were tolerant to drought stress, which was supported by their higher transcript levels of catalase gene (CAT), superoxide dismutase genes (Cu/ZN-SOD, Cu/Zn-SDC) in these cultivars. The downregulation of PDH1 gene (Proline dehydrogenase 1) was also observed that was associated with upregulation of proline accumulation in carrot plants. Moreover, results also suggested that PRT genes (Proline transporter genes) played a key role in drought tolerance in carrot cultivars. Conclusion Among the cultivars studied, Coral Orange showed overall tolerance to drought stress conditions, whereas cultivars Cosmic Purple and Eregli Black were sensitive based on their biochemical and gene expression levels. According to our knowledge, this is the first comparative study on drought tolerance in several carrot cultivars. It will provide a background for carrot breeding to understand biochemical and molecular responses of carrot plant to drought stress and mechanisms behind it.

Comparative transcriptomics of drought stress response of taproot meristem region of contrasting purple carrot breeding lines supported by physio-biochemical parameters.

Carrot is one of the nutritious vegetable crops sensitive to drought stress resulting in loss of quality and yield. There are a lot of studies on detailed molecular mechanisms of drought stress response of main crops; however, very little information available on vegetables, including carrots. Hence, in this study, we investigated root transcriptome profiles from the meristematic region of two contrasting purple carrot (B7262A, drought tolerant; P1129, drought sensitive) lines under varying stress levels (85% and 70%) by using RNA-Seq technique. The morpho-physiological and biochemical response of B7262A line exhibited tolerance behavior to both DS (85% and 70%). RNA-Seq analysis revealed that 15,839 genes were expressed commonly in both carrot lines. The carrot line B7262A showed regulation of 514 genes in response to 85% DS, whereas P1129 showed differential regulation of 622 genes under 70% DS. The B7262A carrot line showed higher upregulation of transcripts that suggested its resilient behavior contrary to P1129 line. Furthermore, validation of transcript gene by qRT-PCR also confirmed the RNA-Seq analysis resulting in elevated expression levels of MYB48 transcription factor, MAPK mitogen-activated protein kinase ANP1, GER geraniol 8-hydroxylase, ABA ABA-induced in somatic embryo 3, FBOX putative F-box protein, FRO ferric reduction oxidase, and PDR probable disease resistance protein. Current study provided unprecedented insights of purple carrot lines that can be potentially exploited for the screening and development of resilient carrot.

Combined drought and heat stresses trigger different sets of miRNAs in contrasting potato cultivars.

MicroRNAs are small, non-coding RNAs that are responsible for regulation of gene expression during plant growth and development. Although there are many studies on miRNAs in other plants, little work has been done to understand the role of miRNAs in abiotic stress tolerance in potatoes. This study investigates changes in miRNA profiles of two different potato cultivars (tolerant, Unica and susceptible, Russet Burbank) in response to heat, drought and their combination. Transcriptomic studies revealed that miRNA profiles depend on the susceptibility and tolerance of the cultivar and also the stress conditions. Large number of miRNAs were expressed in Unica, whereas Russet Burbank indicated lesser number of changes in miRNA expression. Physiological and transcriptional results clearly supported that Unica cultivar is tolerant to combined drought and heat stress compared to Russet Burbank. Moreover, psRNATarget analysis predicted that major miRNAs identified were targeting genes playing important roles in response to drought and heat stress and their important roles in genetic and post-transcriptional regulation, root development, auxin responses and embryogenesis were also observed. This study focused on eight miRNAs (Novel_8, Novel_9, Novel_105, miR156d-3p, miR160a-5p, miR162a-3p, miR172b-3p and miR398a-5p) and their putative targets where results indicate that they may play a vital role at different post-transcriptional levels against drought and heat stresses. We suggest that miRNA overexpression in plants can lead to increased tolerance against abiotic stresses; furthermore, there should be more emphasis on the studies to investigate the role of miRNAs in combined abiotic stress in plants.