The propensity for polyphosphorylation makes myo-inositol derivatives, the inositol polyphosphates (InsPs), especially phytic acid or inositol hexakisphosphate (InsP 6 ) the major form of phosphate storage in plants. Acts of pyrophosphorylation on InsP 6 generates InsP 7 or InsP 8 containing high-energy phosphoanhydride bonds that are harnessed during energy requirements of a cell. Also implicated as co-factors for several phytohormone signaling networks, InsP 7 /InsP 8 modulate key developmental processes. With recent identification as the common moeity for transducing both jasmonic acid (JA) and phosphate-starvation responses (PSR), InsP 8 is the classic example of a metabolite that may moonlight crosstalks to different cellular pathways during diverse stress adaptations. We show here that Arabidopsis thalianaand DIPHOSPHOINOSITOL PENTAKISPHOSPHATE KINASE 2 (VIH2), but not other InsP-kinases, suppress basal salicylic acid (SA)-dependent immunity. In ipk1, itpk1 or vih2 mutants, elevated endogenous SA levels and constitutive activation of defense signaling lead to enhanced resistance against the virulent Pseudomonas syringae pv tomato DC3000 (PstDC3000) strain. Our data reveal that activated SA-signaling sectors in these mutants modulate expression amplitudes of .

Nucleic acid transfer between plants is a phenomenon which is likely to occur in many ways in nature. We report here the active transmission of Apple scar skin viroid (ASSVd) naked ssRNA species by the whitefly Trialeurodes vaporariorum (Tv). Not only the viroid RNA, its DNA form was also identified from the insect. The viroid transfer efficiency was enhanced with the help of Cucumis sativus Phloem protein 2 (CsPP2), a plant protein known to translocate viroid RNAs. This PP2/ASSVd complex is stably present in the viroid infected cucumber plants, as was identified with the help of immunological reaction. As viroid-like secondary structures are found in some plant RNAs, and PP2 is known to bind and translocate several RNAs, the results have huge implications in transfer of these RNA species between plants visited by the whitefly.

Targeted protein degradation is essential for physiological development and adaptation to stress. Mammalian INOSITOL PENTAKISPHOSPHATE KINASE (IP5K) and INOSITOL HEXAKISPHOSPHATE KINASE 1 (IP6K1) pair modulates functions of Cullin RING Ubiquitin E3 ligases (CRLs) that execute targeted degradation of substrates. Coordinated activities of these kinases protect CRLs on a COP9 signalosome (CSN) platform and stimulates deneddylation-dependent disassembly to maintain continuity of its functions. In plants, CRL regulations on CSN by inositol phosphate (InsP) kinases are not known. Here, we show interactions of Arabidopsis thaliana INOSITOL PENTAKISPHOSPHATE 2-KINASE 1 (IPK1) and INOSITOL 1,3,4-TRISPHOSPHATE 5/6-KINASE 1 (ITPK1), counterparts of the above InsP-kinase pair, with CSN subunits and its positive influences on the dynamics of cullin deneddylation. We identify neddylation enhancements on CRLs as an early response to phosphate-starvation and its orchestration by perturbed IPK1/ITPK1 activities. At a molecular level, specific kinetics of CSN5 deneddylase is affected by the above InsP-kinases. Overall, our data reveal conserved InsP-kinase involvements on CRL-CSN synergism in plants.

Apple scar skin viroid (ASSVd) is the type member of the genus Apscaviroid of the family Pospiviroidae and is known to cause scarring and dappling of apple fruits. The herbaceous host range of ASSVd was identified using an infectious dimeric clone. Among 13 plant species inoculated with the viroid, nine were found to be systemic hosts and three served as indicator hosts. The viroid could be transferred to these hosts through agroinoculation, rubbing of dimeric RNA transcripts, dimeric DNA plasmids and through sap inoculation. Single-strand confirmation polymorphism (SSCP) analysis of the progeny obtained after inoculation of the infectious ASSVd clone showed the presence of four sequence variants (V1, V2, V3 and V4) which was also confirmed by sequencing. Two sequence variants (V1 and V3) were identified as dominant, representing 47Á72 and 36Á36% of the total progeny, respectively. The V4 sequence variant was similar to the wild type and occurred at a frequency of only 4Á5% of the total progeny.