24Small RNAs (sRNAs) that are 21 to 24 nucleotides (nt) in length are found in most 25 eukaryotic organisms and regulate numerous biological functions, including transposon 26 silencing, development, reproduction, and stress responses, typically via control of the 27 stability and/or translation of target mRNAs. Major classes of sRNAs in plants include 28 microRNAs (miRNAs) and small interfering RNAs (siRNAs); sRNAs are known to travel 29 as a silencing signal from cell to cell, root to shoot, and even between host and pathogen. 30In mammals, sRNAs are transported inside extracellular vesicles (EVs), which are mobile 31 lipid compartments that participate in intercellular communication. In addition to sRNAs, 32EVs carry proteins, lipids, metabolites, and potentially other types of nucleic acids. Here 33 we report that plant EVs also contain diverse species of sRNA. We found that specific 34 miRNAs and siRNAs are preferentially loaded into plant EVs. We also report a previously 35 overlooked class of "tiny RNAs" (10 to 17 nt) that are highly enriched in EVs. This new 36RNA category of unknown function has a broad and very diverse genome origin and might 37 correspond to degradation products. 39Small RNAs (sRNAs) are important 21 to 24 nucleotide (nt) non-coding signaling 40 molecules involved in a wide variety of processes, including plant development, 41 reproduction and defense (Samad et al., 2017). sRNAs can be divided into two 42 categories, microRNAs (miRNAs) and small interfering RNAs (siRNAs), based on the 43 differences in their biogenesis and mode of action. miRNAs originate from a single-44 stranded, self-complementary, non-coding RNA that forms a hairpin structure. In contrast, 45 siRNAs originate from a double-stranded RNA molecule synthesized by RNA-46 DEPENDENT RNA POLYMERASES (RDRs). siRNAs can further be divided into two 47 main categories, heterochromatic siRNAs (hc-siRNAs) and phased siRNAs, including 48 trans-acting siRNAs (tasi-RNAs). Both of these double-stranded RNA structures are 49 recognized by Dicer-like proteins (DCL), which cleave these RNAs into defined length 50 products. One strand of these products is then selectively loaded onto an ARGONAUTE 51 (AGO) protein and incorporated into the RNA-induced Silencing Complex (RISC). The 52 RISC uses the sRNA in a sequence-homology-dependent manner to negatively regulate 53 targets, typically mRNAs (Borges and Martienssen, 2015). 54 sRNAs are often mobile and function in non-cell autonomous silencing, which can 55 be either local or systemic. Local RNA silencing occurs among groups of adjacent cells 56 and can gradually spread from cell to cell (Marín-González and Suárez-López, 2012; 57 Dunoyer et al., 2013). Systemic silencing occurs over long distances and can spread 58 throughout an entire plant. While there are several documented cases of mobile small 59RNAs in plants, the mechanisms by which these RNAs move has yet to be clearly 60 established. Local RNA silencing is thought to involve the transport of RNAs through 61 plasmodesmata (PD) wi...
Soil salinity is one of the most serious environmental factors that affect crop productivity worldwide. Inevitable global climate change leading to rise in sea water level would exacerbate degradation of irrigation systems and contamination of ground water resources, which render conventional agricultural practices impossible due to the sensitivity of most crops to salinity. Breeding for development of salt-tolerant crop plants has been a major challenge due to the complexity and multigenic control of salt tolerance traits. Halophytes are capable of surviving and thriving under salt at concentrations as high as 5 g/L, by maintaining negative water potential. Physiological and molecular studies have suggested that halophytes, unlike glycophytes, have evolved mechanisms, such as ion homeostasis through ion extrusion and compartmentalization, osmotic adjustments, and antioxidant production for adaptation to salinity. Employment of integrated approaches involving different omics tools would amplify our understanding of the biology of stress response networks in the halophytes. Translation of the knowledge and resources generated from halophyte relatives of crop plants through functional genomics will lead to the development of new breeds of crops that are suitable for saline agriculture.
Expression patterns of four candidate AREB/ABF genes and four DREB/CBF genes were evaluated in leaf and root tissues of five grape varieties (‘Qalati’, ‘Kaj Angoor’, ‘Sabz Angoor’, ‘Siahe Zarghan’, ‘Bidane Safid’) with differential response to drought stress. Among the AREB/ABF genes, AREB1 and ABF2 showed up-regulation in response to drought stress in leaf and root tissues of all varieties while AREB2 and ABF1 showed down-regulation in both leaf and root tissues of the sensitive variety ‘Bidane Sefid’ in response to drought and salt stress. Among the DREB/CBF genes, CBF4 was the most responsive to drought stress in both leaf and root tissues. CBF2 and CBF3 showed up-regulation in all varieties in response to drought stress in leaf except in ‘Bidane Sefid’. Under salinity stress, AREB2 and ABF2 showed up-regulation in response to the increasing level of salinity in the leaf tissues but in the root tissues ABF2 was up-regulated in response to increasing NaCl concentration while AREB2 was down-regulated. Therefore, it seems AREB2 has tissue-specific response to salinity stress. All CBF genes were up-regulated in response to salinity stress in the leaf and root tissues. Expression data suggested that CBF2 is more responsive to NaCl stress. Among all four promising and stress tolerant varieties ‘Siah Zarghan’ and ‘Kaj Angoor’ were more tolerant than ‘Qalati’ and ‘Sabz Angoor’ to drought and salinity.
ADP-ribosylation factors (ARFs) have been reported to function in diverse physiological and molecular activities. Recent evidences also demonstrate the involvement of ARFs in conferring tolerance to biotic and abiotic stresses in plant species. In the present study, 23 and 25 ARF proteins were identified in C3 model- rice and C4 model- foxtail millet, respectively. These proteins are classified into four classes (I–IV) based on phylogenetic analysis, with ARFs in classes I–III and ARF-like proteins (ARLs) in class IV. Sequence alignment and domain analysis revealed the presence of conserved and additional motifs, which may contribute to neo- and sub-functionalization of these proteins. Promoter analysis showed the presence of several cis-regulatory elements related to stress and hormone response, indicating their role in stress regulatory network. Expression analysis of rice ARFs and ARLs in different tissues, stresses and abscisic acid treatment highlighted temporal and spatial diversification of gene expression. Five rice cultivars screened for allelic variations in OsARF genes showed the presence of allelic polymorphisms in few gene loci. Altogether, the study provides insights on characteristics of ARF/ARL genes in rice and foxtail millet, which could be deployed for further functional analysis to extrapolate their precise roles in abiotic stress responses.
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