@article {125201, title = {Indian Himalayan natural Arabidopsis thaliana accessions with abolished miR158 levels exhibit robust miR173-initiated trans-acting cascade silencing.}, journal = {Plant J}, year = {2023}, month = {2023 Mar 08}, abstract = {

Small RNAs such as microRNAs (miRNAs) and small interfering (si)RNAs are short 20-24-nucleotide non-coding RNAs. They are key regulators of gene expression in plants and other organisms. Several 22-nucleotide long miRNAs trigger biogenesis of cascades of trans-acting secondary small interfering RNAs, involved in various developmental and stress responses. Here we show that in Himalayan Arabidopsis thaliana accessions having natural mutations in miR158 locus exhibit robust cascade silencing in pentatricopeptide (PPR)-like locus. Furthermore, we show that these cascade sRNAs trigger tertiary silencing of a gene involved in transpiration and stomatal opening. The natural variants of MIR158 having deletions or insertions led to improper processing of miR158 precursors thereby blocking synthesis of mature miR158. Reduced miR158 led to increased level of its target, a pseudo-pentatricopeptide gene that is otherwise targeted by ta-siRNAs generated by miR173 cascade in other accessions. Using small RNA datasets derived from Indian Himalayan accessions, as well as overexpression and knockout lines of miR158, we show that absence of miR158 led to build up of pseudo-PPR derived tertiary small RNAs. These tertiary sRNAs mediated robust silencing of a gene involved in stomatal closure in Himalayan accessions lacking miR158 expression. We functionally validated the tertiary phasiRNA that targets NHX2 a Na -K /H antiporter protein thereby regulating transpiration and stomatal conductance. Overall, we deciphered a new module of sRNA network, miRNA-TAS-siRNA-pseudogene-tertiary phasiRNA-NHX2 in plant adaptation.

}, issn = {1365-313X}, doi = {10.1111/tpj.16175}, author = {Tripathi, Abhinandan Mani and Singh, Rajneesh and Verma, Ashwani Kumar and Singh, Akanksha and Mishra, Parneeta and Dwivedi, Varun and Narayan, Shiv and Sundar, G Vivek Hari and Shirke, Pramod Arvind and Shivaprasad, P V and Roy, Sribash} } @article {113539, title = {An inducible potato (E,E)-farnesol synthase confers tolerance against bacterial pathogens in potato and tobacco.}, journal = {Plant J}, year = {2022}, month = {2022 Jul 02}, abstract = {

Terpene synthases (TPSs) have diverse biological functions in plants. Though the roles of TPSs in herbivore defense are well established in many plant species, their role in bacterial defense has been scarce and is emerging. Through functional genomics, here we report the in planta role of potato (Solanum tuberosum) terpene synthase (StTPS18) in bacterial defense. Expression of StTPS18 was highest in leaves and was induced in response to Pseudomonas syringae and methyl jasmonate treatments. The recombinant StTPS18 exhibited bona fide (E,E)-farnesol synthase activity forming a sesquiterpenoid, (E,E)-farnesol as the sole product, utilising (E,E)-farnesyl diphosphate (FPP). Subcellular localization of GFP fusion protein revealed that StTPS18 is localized to the cytosol. Silencing and overexpression of StTPS18 in potato resulted in reduced and enhanced tolerance, respectively, to bacterial pathogens P. syringae and Ralstonia solanacearum. Bacterial growth assay using medium containing (E,E)-farnesol significantly inhibited P. syringae growth. Moreover, StTPS18 overexpressing transgenic potato and Nicotiana tabacum leaves, and (E,E)-farnesol and P. syringae infiltrated potato leaves exhibited elevated expression of sterol pathway and members of pathogenesis-related genes with enhanced phytosterol accumulation. Interestingly, enhanced phytosterols in C -(E,E)-farnesol infiltrated potato leaves were devoid of any noticeable C labeling, indicating no direct utilization of (E,E)-farnesol in phytosterols formation. Furthermore, leaves of StTPS18 overexpressing transgenic lines had no detectable (E,E)-farnesol similar to the control plant, and emitted lower levels of sesquiterpenes than the control. These findings point towards an indirect involvement of StTPS18 and its product (E,E)-farnesol in bacterial defense through upregulation of phytosterol biosynthesis and defense genes.

}, issn = {1365-313X}, doi = {10.1111/tpj.15890}, author = {Dwivedi, Varun and Kumar, Sarma Rajeev and Shilpashree, H B and Krishna, Ram and Rao, Srinivas and Shasany, Ajit K and Olsson, Shannon B and Nagegowda, Dinesh A} } @article {82441, title = {Functional characterization of a defense-responsive bulnesol/elemol synthase from potato.}, journal = {Physiol Plant}, volume = {171}, year = {2021}, month = {2020 Sep 03}, pages = {7-21}, abstract = {

Terpene synthases (TPSs) produce a variety of terpenoids that play numerous functional roles in primary and secondary metabolism, as well as in ecological interactions. Here, we report the functional characterization of an inducible potato TPS gene encoding bulnesol/elemol synthase (StBUS/ELS). The expression of StBUS/ELS in potato leaves was significantly induced in response to both bacterial (Pseudomonas syringae) and fungal (Alternaria solani) infection as well as methyl jasmonate treatment, indicating its role in defense. The leaves exhibited the highest StBUS/ELS expression followed by the stem with least and similar expression in tuber, sprout and root. Recombinant StBUS/ELS catalyzed the formation of different sesquiterpenes by utilizing farnesyl diphosphate as substrate, and the monoterpene geraniol from geranyl diphosphate. Among the sesquiterpenes formed by StBUS/ELS, elemol was the predominant product followed by α-bulnesene, bulnesol, and β-elemene. Further GC-MS analysis of StBUS/ELS assay products at different injection temperatures revealed elemol and bulnesol as the major products at 275{\textdegree}C and 200/150{\textdegree}C, respectively, without much change in the levels of minor products. This indicated thermal rearrangement of bulnesol into elemol at higher temperatures. Transient overexpression of StBUS/ELS in potato leaves conferred tolerance against the growth of bacteria P. syringae and Ralstonia solanacearum, and the fungus A. solani. Further, expression analysis of pathogenesis-related (PR) genes in StBUS/ELS overexpressing leaves showed no significant change in comparison to control, indicating a direct involvement of StBUS/ELS enzymatic products against pathogens. Overall, our study suggested that StBUS/ELS is a pathogen-inducible TPS encoding bulnesol/elemol synthase and could provide a direct role in defense against biotic stress in potato.

}, issn = {1399-3054}, doi = {10.1111/ppl.13199}, author = {Dwivedi, Varun and Rao, Srinivas and Bomzan, Dikki Pedenla and Kumar, Sarma Rajeev and Shanmugam, Pragadheesh V and Olsson, Shannon B and Nagegowda, Dinesh A} }