Co-expression of stress-responsive regulatory genes, MuNAC4, MuWRKY3 and MuMYB96 associated with resistant-traits improves drought adaptation in transgenic groundnut (Arachis hypogaea l.) plants.

Groundnut, cultivated under rain-fed conditions is prone to yield losses due to intermittent drought stress. Drought tolerance is a complex phenomenon and multiple gene expression required to maintain the cellular tolerance. Transcription factors (TFs) regulate many functional genes involved in tolerance mechanisms. In this study, three stress-responsive regulatory TFs cloned from horse gram, (Macrotyloma uniflorum (Lam) Verdc.), MuMYB96, involved in cuticular wax biosynthesis; MuWRKY3, associated with anti-oxidant defense mechanism and MuNAC4, tangled with lateral root development were simultaneously expressed to enhance drought stress resistance in groundnut (Arachis hypogaea L.). The multigene transgenic groundnut lines showed reduced ROS production, membrane damage, and increased superoxide dismutase (SOD) and ascorbate peroxidase (APX) enzyme activity, evidencing improved antioxidative defense mechanisms under drought stress. Multigene transgenic plants showed lower proline content, increased soluble sugars, epicuticular wax content and higher relative water content suggesting higher maintenance of tissue water status compared to wildype and mock plants. The scanning electron microscopy (SEM) analysis showed a substantial increase in deposition of cuticular waxes and variation in stomatal number in multigene transgenic lines compared to wild type and mock plants. The multigene transgenic plants showed increased growth of lateral roots, chlorophyll content, and stay-green nature in drought stress compared to wild type and mock plants. Expression analysis of transgenes, MuMYB96, MuWRKY3, and MuNAC4 and their downstream target genes, KCS6, KCR1, APX3, CSD1, LBD16 and DBP using qRT-PCR showed a two- to four-fold increase in transcript levels in multigene transgenic groundnut plants over wild type and mock plants under drought stress. Our study demonstrate that introducing multiple genes with simultaneous expression of genes is a viable option to improve stress tolerance and productivity under drought stress.

Small RNA-based interactions between rice and the viruses which cause the tungro disease.

Rice tungro disease is caused by a complex of two viruses, Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV). To examine the RNAi-based defence response in rice during tungro disease, we characterized the virus-derived small RNAs and miRNAs by Deep Sequencing. We found that, while 21 nt/22 nt (nucleotide) siRNAs are predominantly produced in a continuous, overlapping and asymmetrical manner from RTBV, siRNA accumulation from RTSV were negligible. Additionally, 54 previously known miRNAs from rice, predicted to be regulating genes involved in plant defence, hormone signaling and developmental pathways were differentially expressed in the infected samples, compared to the healthy ones. This is the first study of sRNA profile of tungro virus complex from infected rice plants. The biased response of the host antiviral machinery against the two viruses and the differentially-expressed miRNAs are novel observations, which entail further studies.

Bacilliform DNA-containing plant viruses in the tropics: commonalities within a genetically diverse group.

Plant viruses, possessing a bacilliform shape and containing double-stranded DNA, are emerging as important pathogens in a number of agricultural and horticultural crops in the tropics. They have been reported from a large number of countries in African and Asian continents, as well as from islands from the Pacific region. The viruses, belonging to two genera, Badnavirus and Tungrovirus, within the family Caulimoviridae, have genomes displaying a common plan, yet are highly variable, sometimes even between isolates of the same virus. In this article, we summarize the current knowledge with a view to revealing the common features embedded within the genetic diversity of this group of viruses. TAXONOMY: Virus; order Unassigned; family Caulimoviridae; genera Badnavirus and Tungrovirus; species Banana streak viruses, Bougainvillea spectabilis chlorotic vein banding virus, Cacao swollen shoot virus, Citrus yellow mosaic badnavirus, Dioscorea bacilliform viruses, Rice tungro bacilliform virus, Sugarcane bacilliform viruses and Taro bacilliform virus. MICROBIOLOGICAL PROPERTIES: Bacilliform in shape; length, 60-900 nm; width, 35-50 nm; circular double-stranded DNA of approximately 7.5 kbp with one or more single-stranded discontinuities. HOST RANGE: Each virus generally limited to its own host, including banana, bougainvillea, black pepper, cacao, citrus species, Dioscorea alata, rice, sugarcane and taro. DISEASE SYMPTOMS: Foliar streaking in banana and sugarcane, swelling of shoots in cacao, yellow mosaic in leaves and stems in citrus, brown spot in the tubers in yam and yellow-orange discoloration and stunting in rice. USEFUL WEBSITES: http://www.dpvweb.net.

Sequencing and computational analysis of complete genome sequences of Citrus yellow mosaic badna virus from acid lime and pummelo.

Citrus yellow mosaic badna virus (CMBV), a member of the Family Caulimoviridae, Genus Badnavirus, is the causative agent of Citrus mosaic disease in India. Although the virus has been detected in several citrus species, only two full-length genomes, one each from Sweet orange and Rangpur lime, are available in publicly accessible databases. In order to obtain a better understanding of the genetic variability of the virus in other citrus mosaic-affected citrus species, we performed the cloning and sequence analysis of complete genomes of CMBV from two additional citrus species, Acid lime and Pummelo. We show that CMBV genomes from the two hosts share high homology with previously reported CMBV sequences and hence conclude that the new isolates represent variants of the virus present in these species. Based on in silico sequence analysis, we predict the possible function of the protein encoded by one of the five ORFs.