Genome-wide analysis was carried out to identify and analyze differential expression pattern of tomato membrane bound NAC transcription factors (SlNACMTFs) during stresses. Two biotic-stress-related SlNACMTFs have been characterized to elucidate their regulatory function. NAC transcription factors are known regulators of stress-related gene expression. As Stresses are perceived and transmitted by membrane-bound proteins, functional characterization of membrane-associated NAC transcription factors in tomato can reveal valuable insight about membrane-mediated stress-signalling. Tomato genome encodes 13 NAC genes which have predicted transmembrane domain(s) (SlNACMTFs). mRNA of 12 SlNACMTFs were readily detected in multiple tissues, and also in polysome isolated from leaf, confirming active transcription and translation from these genes occur under normal physiological condition. Additionally, most of the SlNACMTFs were differentially regulated during stresses and stress-related transcription factor binding sites are prevalent in their promoters. SlNACMTF3 and 8 were majorly regulated in biotic and abiotic stresses. Like other MTFs, SlNACMTF3 was translocated to the plasma membrane, whereas the C-terminus truncated (ΔC) form localized in the cytoplasm and the nucleus. Accordingly, the ΔC forms significantly influenced the activity of promoters harbouring NAC binding sites (NACbs). Furthermore, the NAC domain of these transcription factors could directly interact with an NACbs, and the proteins failed to regulate a promoter lacking a crucial NACbs. Interestingly, the type of influence to an NACbs containing promoter was dependent on the context of the NACbs, as the same SlNACMTF showed an alternative mode of regulation on different promoters, as well as the same promoter activity was oppositely regulated by two different SlNACMTF. Finally, both SlNACMTFs demonstrated the differential regulatory effect on the expression of several stress-related genes by interacting with the putative NACbs in their promoter region, suggesting their direct role in plant stress response.

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Armadillo repeat family is well-characterized in several plant species for their involvement in multiple regulatory processes including growth, development, and stress response. We have previously shown a three-fold higher expression of ARM protein-encoding in tomato cultivar tolerant to tomato leaf curl New Delhi virus (ToLCNDV) compared to susceptible cultivar upon virus infection. This suggests the putative involvement of ARM proteins in defense response against virus infection; however, no comprehensive investigation has been performed to address this inference. In the present study, we have identified a total of 46 ARM-repeat proteins (SlARMs), and 41 U-box-containing proteins (SlPUBs) in tomato. These proteins and their corresponding genes were studied for their physicochemical properties, gene structure, domain architecture, chromosomal localization, phylogeny, and cis-regulatory elements in the upstream promoter region. Expression profiling of candidate genes in response to ToLCNDV infection in contrasting tomato cultivars showed significant upregulation of SlARM18 in the tolerant cultivar. Virus-induced gene silencing of SlARM18 in the tolerant tomato cultivar conferred susceptibility, which suggests the involvement of this gene in resistance mechanism. Further studies are underway to functionally characterize SlARM18 to delineate its precise role in defense mechanism.

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Begomovirus infection in plant causes a great economic loss in many countries every year. Increasing rate of the infectivity of this single stranded DNA virus forces to study of its transmission in detail for the necessary researches regarding the control of this disease. This pathogenic virus is whitefly vector borne and transferred from one plant to another plant during the suckling of phloem sap by that vector. Viral transmissibility through this insect vector may depend on the genetic variations within the cryptic species groups. Two distinct categories of begomoviruses viz., bipartite and monopartite types consist of different genome organization. Virion particles modify the intracellular environment of the host according to their need of replication and survival. Viral replication takes place through RCR as well as RDR methods. Interplay among host, vector and pathogen is crucial for the establishment of infection. Several endosymbiotic organisms living within the insect vector also have vital role here. Being infected with this virus, host plant responds with defensive activities like TGS, PTGS, autophagy, hormonal regulation, metabolic alteration etc. However, virus also counteracts those through the manipulation of several pathways of cellular events. It is necessary to study in different directions and utilize advanced molecular biological techniques to develop begomovirus resistance within plants.

Vascular development-related TRN1 transcription is suppressed by cytosine methylation in growing leaves of tomato. ToLCNDV infection disrupts methylation machinery and reactivates TRN1 expression -likely leading to symptom manifestation.