The SlNAC2 transcription factor from tomato confers tolerance to drought stress in transgenic tobacco plants.

Drought is a key environmental factor that restricts crop growth and productivity. Plant responses to water-deficit stress at the whole plant level are mediated by stress-response gene expression through the action of transcription factors (TF). The NAC (NAM/ATAF/CUC) transcription factor family has been well documented in its role in improving plant abiotic stress tolerance. In the present study we evaluated the effects of overexpression of SlNAC2 TF on the photosynthetic machinery, relative water content (RWC), reactive oxygen species, antioxidants and proline levels in tobacco plants exposed to a water-deficit treatment. Shoot growth and seed formation were also evaluated before, during and following water-deficit to determine any morphological consequences of transgene expression. The transgenic plants maintained higher RWC and chlorophyll levels over 21 days after withholding water and stomatal conductance until the 16th day of water-deficit. Overexpression of SlNAC2 in tobacco increased proline levels, improved seed setting and delayed leaf senescence of the transgenic plants. Reactive oxygen species accumulated at lower levels in the dehydrated transgenic plants but no significant difference in superoxide dismutase and catalase content were seen between the genotypes. The conversion of glutathione to oxidized glutathione was significantly higher in the transgenic plants, supported by increased glutathione reductase transcript levels. Our results indicate that overexpression of SlNAC2 in tobacco improved survival during and recovery from water-deficit stress, without an associated biomass penalty under irrigation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-021-00996-2.

Discovery of genomic regions and candidate genes for grain weight employing next generation sequencing based QTL-seq approach in rice (Oryza sativa L.).

Rice (Oryza sativa L.) yield enhancement is one of the prime objectives of plant breeders. Elucidation of the inheritance of grain weight, a key yield component trait, is of paramount importance for raising the yield thresholds in rice. In the present investigation, we employed Next-Generation Sequencing based QTL-seq approach to identify major genomic regions associated with grain weight using mapping populations derived from a cross between BPT5204 and MTU3626. QTL-seq analysis identified three grain weight quantitative trait loci (QTL) viz., qGW1 (35-40 Mb), qGW7 (10-18 Mb), and qGW8 (2-5 Mb) on chromosomes 1, 7 and 8, respectively and all are found to be novel. Further, qGW8 was confirmed through conventional QTL mapping in F2, F3 and BC1F2 populations and found to explain the phenotypic variance of 17.88%, 16.70% and 15.00%, respectively, indicating a major QTL for grain weight. Based on previous reports, two candidate genes in the qGW8 QTL were predicted i.e., LOC_Os08g01490 (Cytochrome P450), and LOC_Os08g01680 (WD domain, G-beta repeat domain containing protein) and through in silico analysis they were found to be highly expressed in reproductive organs during different stages of grain development. Here, we have demonstrated that QTL-seq is one of the rapid approaches to uncover novel QTLs controlling complex traits. The candidate genes identified in the present study undoubtedly enhance our understanding of the mechanism and inheritance of the grain weight. These candidate genes can be exploited for yield enhancement after confirmation through complementary studies.

Cross-genera amplification of Cajanus spp. specific SSR markers in Clitoria ternatea (L.) and their application in genetic diversity studies.

Clitoria ternatea (L.) is a medicinal leguminous plant and is cultivated to cater the need of herbal industries and asthetic purposes. The unavailability of steady molecular marker impedes the genetic improvement of C. ternatea. In the present study, transferability of 98 pairs of Cajanus spp. specific SSR primers were assessed among 14 genotypes of C. ternatea, varied for their flower color, floral architecture and bio-metabolite (taraxerol and delphinidin) content, and out of them 43 had successfully amplified the fragments. Among them, 36 pairs of primers showed 100% transferability, whereas rest seven varied from 42.86 to 92.85% transferability. The transferable 43 pairs of SSR primers generated 196 alleles across the 14 genotypes and the AMOVA analysis showed moderate genetic variation (55.1%) among the genotypes of C. ternatea, which was also reinforced by Nei's genetic distance and gene identity estimates derived haplotype matrix. Similarly, both the principal coordinate analysis and dendrogram grouped these 14 genotypes of C. ternatea into two major clusters based on SSR allele distribution and frequency, and the clustering pattern is in accordance with petal color but in contrast to floral architecture. MCheza based outlier analysis revealed 16 alleles for balancing selection, which are putatively involved in the maintenance of genetic polymorphism in C. ternatea. Moreover, the estimates of molecular diversity and bio-metabolite content revealed the possible use of these genotypes in future breeding programme of this species.

Transcriptional Regulation of Aluminum-Tolerance Genes in Higher Plants: Clarifying the Underlying Molecular Mechanisms.

Aluminum (Al) rhizotoxicity is one of the major environmental stresses that decrease global food production. Clarifying the molecular mechanisms underlying Al tolerance may contribute to the breeding of Al-tolerant crops. Recent studies identified various Al-tolerance genes. The expression of these genes is inducible by Al. Studies of the major Arabidopsis thaliana Al-tolerance gene, ARABIDOPSIS THALIANA ALUMINUM-ACTIVATED MALATE TRANSPORTER 1 (AtALMT1), which encodes an Al-activated malate transporter, revealed that the Al-inducible expression is regulated by a SENSITIVE TO PROTON RHIXOTOXICITY 1 (STOP1) zinc-finger transcription factor. This system, which involves STOP1 and organic acid transporters, is conserved in diverse plant species. The expression of AtALMT1 is also upregulated by several phytohormones and hydrogen peroxide, suggesting there is crosstalk among the signals involved in the transcriptional regulation of AtALMT1. Additionally, phytohormones and reactive oxygen species (ROS) activate various transcriptional responses, including the expression of genes related to increased Al tolerance or the suppression of root growth under Al stress conditions. For example, Al suppressed root growth due to abnormal accumulation of auxin and cytokinin. It activates transcription of TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1 and other phytohormone responsive genes in distal transition zone, which causes suppression of root elongation. On the other hand, overexpression of Al inducible genes for ROS-detoxifying enzymes such as GLUTATHIONE-S-TRANSFERASE, PEROXIDASE, SUPEROXIDE DISMUTASE enhances Al resistance in several plant species. We herein summarize the complex transcriptional regulation of an Al-inducible genes affected by STOP1, phytohormones, and ROS.