Role of the gibberellin receptors GID1 during fruit‐set in Arabidopsis

Gibberellins (GAs) play a critical role in fruit‐set and fruit growth. Gibberellin is perceived by its nuclear receptors GA INSENSITIVE DWARF1s (GID1s), which then trigger degradation of downstream repressors DELLAs. To understand the role of the three GA receptor genes (GID1A, GID1B and GID1C) in Arabidopsis during fruit initiation, we have examined their temporal and spatial localization, in combination with analysis of mutant phenotypes. Distinct expression patterns are revealed for each GID1: GID1A is expressed throughout the whole pistil, while GID1B is expressed in ovules, and GID1C is expressed in valves. Functional study of gid1 mutant combinations confirms that GID1A plays a major role during fruit‐set and growth, whereas GID1B and GID1C have specific roles in seed development and pod elongation, respectively. Therefore, in ovules, GA perception is mediated by GID1A and GID1B, while GID1A and GID1C are involved in GA perception in valves. To identify tissue‐specific interactions between GID1s and DELLAs, we analyzed spatial expression patterns of four DELLA genes that have a role in fruit initiation (GAI, RGA, RGL1 and RGL2). Our data suggest that GID1A can interact with RGA and GAI in all tissues, whereas GID1C–RGL1 and GID1B–RGL2 interactions only occur in valves and ovules, respectively. These results uncover specific functions of each GID1–DELLA in the different GA‐dependent processes that occur upon fruit‐set. In addition, the distribution of GA receptors in valves along with lack of expression of GA biosynthesis genes in this tissue, strongly suggests transport of GAs from the developing seeds to promote fruit growth.     

CsSPL functions as an adaptor between HD‐ZIP III and CsWUS transcription factors regulating anther and ovule development in Cucumis sativus (cucumber)

Anther and ovule genesis preconditions crop fertilization and fruit production; however, coordinative regulation of anther and ovule development and underlying molecular pathways remain largely elusive. Here, we found that SPOROCYTELESS (SPL)/NOZZLE (NZZ) expression was nearly abolished in a Cucumis sativus (cucumber) mutant with severely defective anther and ovule development. CsSPL was expressed specifically in the developing anthers and ovules. Knock‐down of CsSPL reduced male and female fertility with malformed pollen and suppressed ovule development. Importantly, CsSPL directly interacted with CsWUS (WUSCHEL) in the nucellus and YABBY family genes in integuments, and positively regulated CsWUS expression, meanwhile the HD‐ZIP III gene CsPHB (PHABULOSA), expressed specifically in the nucellus, promoted CsSPL expression by binding to the CsSPL promoter. Thus, CsSPL acts as an adaptor to link CsPHB and CsWUS functioning, underpinning a previously unidentified regulatory pathway orchestrating sex organ development in planta. In addition, auxin accumulation was reduced in the reproductive organs of CsSPL knock‐down plants. Biochemical analyses further showed that CsSPL stimulated the expression of AUXIN RESPONSE FACTOR 3 (CsARF3), and was positively regulated by CsARF13 during reproductive organ development, indicating sequential interactions of CsSPL with auxin signaling components in orchestrating anther and ovule development.     

microRNA159‐targeted SlGAMYB transcription factors are required for fruit set in tomato

The transition from flowering to fruit production, namely fruit set, is crucial to ensure successful sexual plant reproduction. Although studies have described the importance of hormones (i.e. auxin and gibberellins) in controlling fruit set after pollination and fertilization, the role of microRNA‐based regulation during ovary development and fruit set is still poorly understood. Here we show that the microRNA159/GAMYB1 and ‐2 pathway (the miR159/GAMYB1/2 module) is crucial for tomato ovule development and fruit set. MiR159 and SlGAMYBs were expressed in preanthesis ovaries, mainly in meristematic tissues, including developing ovules. SlMIR159‐overexpressing tomato cv. Micro‐Tom plants exhibited precocious fruit initiation and obligatory parthenocarpy, without modifying fruit shape. Histological analysis showed abnormal ovule development in such plants, which led to the formation of seedless fruits. SlGAMYB1/2 silencing in SlMIR159‐overexpressing plants resulted in misregulation of pathways associated with ovule and female gametophyte development and auxin signalling, including AINTEGUMENTA‐like genes and the miR167/SlARF8a module. Similarly to SlMIR159‐overexpressing plants, SlGAMYB1 was downregulated in ovaries of parthenocarpic mutants with altered responses to gibberellins and auxin. SlGAMYBs likely contribute to fruit initiation by modulating auxin and gibberellin responses, rather than their levels, during ovule and ovary development. Altogether, our results unveil a novel function for the miR159‐targeted SlGAMYBs in regulating an agronomically important trait, namely fruit set.     

Two‐step d‐ononitol epimerization pathway in Medicago truncatula

Methylated inositol, d ‐pinitol (3‐O‐methyl‐d ‐chiro‐inositol), is a common constituent in legumes. It is synthesized from myo‐inositol in two reactions: the first reaction, catalyzed by myo‐inositol‐O‐methyltransferase (IMT), consists of a transfer of a methyl group from S‐adenosylmethionine to myo‐inositol with the formation of d ‐ononitol, while the second reaction, catalyzed by d ‐ononitol epimerase (OEP), involves epimerization of d ‐ononitol to d ‐pinitol. To identify the genes involved in d ‐pinitol biosynthesis in a model legume Medicago truncatula, we conducted a BLAST search on its genome using soybean IMT cDNA as a query and found putative IMT (MtIMT) gene. Subsequent co‐expression analysis performed on publicly available microarray data revealed two potential OEP genes: MtOEPA, encoding an aldo‐keto reductase and MtOEPB, encoding a short‐chain dehydrogenase. cDNAs of all three genes were cloned and expressed as recombinant proteins in E. coli. In vitro assays confirmed that putative MtIMT enzyme catalyzes methylation of myo‐inositol to d ‐ononitol and showed that MtOEPA enzyme has NAD⁺‐dependent d ‐ononitol dehydrogenase activity, while MtOEPB enzyme has NADP⁺‐dependent d ‐pinitol dehydrogenase activity. Both enzymes are required for epimerization of d ‐ononitol to d ‐pinitol, which occurs in the presence of NAD⁺ and NADPH. Introduction of MtIMT, MtOEPA, and MtOEPB genes into tobacco plants resulted in production of d ‐ononitol and d ‐pinitol in transformants. As this two‐step pathway of d ‐ononitol epimerization is coupled with a transfer of reducing equivalents from NADPH to NAD⁺, we speculate that one of the functions of this pathway might be regeneration of NADP⁺ during drought stress.     

AGAMOUS‐LIKE13, a putative ancestor for the E functional genes,specifies male and female gametophyte morphogenesis

Arabidopsis AGL13 is a member of the AGL6 clade of the MADS box gene family. GUS activity was specifically detected from the initiation to maturation of both pollen and ovules in AGL13:GUS Arabidopsis. The sterility of the flower with defective pollen and ovules was found in AGL13 RNAi knockdown and AGL13 + SRDX dominant‐negative mutants. These results indicate that AGL13 acts as an activator in regulation of early initiation and further development of pollen and ovules. The production of similar floral organ defects in the severe AGL13 + SRDX and SEP2 + SRDX plants and the similar enhancement of AG nuclear localization efficiency by AGL13 and SEP3 proteins suggest a similar function for AGL13 and E functional SEP proteins. Additional fluorescence resonance energy transfer (FRET) analysis indicated that, similar to SEP proteins, AGL13 is able to interact with AG to form quartet‐like complexes (AGL13–AG)₂ and interact with AG–AP3–PI to form a higher‐order heterotetrameric complex (AGL13–AG–AP3–PI). Through these complexes, AGL13 and AG could regulate the expression of similar downstream genes involved in pollen morphogenesis, anther cell layer formation and the ovule development. AGL13 also regulates AG/AP3/PI expression by positive regulatory feedback loops and suppresses its own expression through negative regulatory feedback loops by activating AGL6, which acts as a repressor of AGL13. Our data suggest that AGL13 is likely a putative ancestor for the E functional genes which specifies male and female gametophyte morphogenesis in plants during evolution.     

The diversion of 2‐C‐methyl‐d‐erythritol‐2,4‐cyclodiphosphate from the 2‐C‐methyl‐d‐erythritol 4‐phosphate pathway to hemiterpene glycosides mediates stress responses in Arabidopsis thaliana

2‐C‐Methyl‐d ‐erythritol‐2,4‐cyclodiphosphate (MEcDP) is an intermediate of the plastid‐localized 2‐C‐methyl‐d ‐erythritol‐4‐phosphate (MEP) pathway which supplies isoprenoid precursors for photosynthetic pigments, redox co‐factor side chains, plant volatiles, and phytohormones. The Arabidopsis hds‐3 mutant, defective in the 1‐hydroxy‐2‐methyl‐2‐(E)‐butenyl‐4‐diphosphate synthase step of the MEP pathway, accumulates its substrate MEcDP as well as the free tetraol 2‐C‐methyl‐d ‐erythritol (ME) and glucosylated ME metabolites, a metabolic diversion also occurring in wild type plants. MEcDP dephosphorylation to the free tetraol precedes glucosylation, a process which likely takes place in the cytosol. Other MEP pathway intermediates were not affected in hds‐3. Isotopic labeling, dark treatment, and inhibitor studies indicate that a second pool of MEcDP metabolically isolated from the main pathway is the source of a signal which activates salicylic acid induced defense responses before its conversion to hemiterpene glycosides. The hds‐3 mutant also showed enhanced resistance to the phloem‐feeding aphid Brevicoryne brassicae due to its constitutively activated defense response. However, this MEcDP‐mediated defense response is developmentally dependent and is repressed in emerging seedlings. MEcDP and ME exogenously applied to adult leaves mimics many of the gene induction effects seen in the hds‐3 mutant. In conclusion, we have identified a metabolic shunt from the central MEP pathway that diverts MEcDP to hemiterpene glycosides via ME, a process linked to balancing plant responses to biotic stress.     

Breeding systems in Cyrtanthus (Amaryllidaceae): variation in self‐sterility and potential for ovule discounting

• Breeding systems of plants determine their reliance on pollinators and ability to produce seeds following self‐pollination. Self‐sterility, where ovules that are penetrated by self‐pollen tubes that do not develop into seeds, is usually considered to represent either a system of late‐acting self‐incompatibility or strong early inbreeding depression. Importantly, it can lead to impaired female function through ovule or seed discounting when stigmas receive mixtures of self and cross pollen, unless cross pollen is able to reach the ovary ahead of self pollen (‘prepotency’). Self‐sterility associated with ovule penetration by self‐pollen tubes appears to be widespread among the Amaryllidaceae.
• We tested for self‐sterility in three Cyrtanthus species – C. contractus, C. ventricosus and C. mackenii – by means of controlled hand‐pollination experiments. To determine the growth rates and frequency of ovule penetration by self‐ versus cross‐pollen tubes, we used fluorescence microscopy to examine flowers of C. contractus harvested 24, 48 and 72 h after pollination, in conjunction with a novel method of processing these images digitally. To test the potential for ovule discounting (loss of cross‐fertilisation opportunities when ovules are disabled by self‐pollination), we pollinated flowers of C. contractus and C. mackenii with mixtures of self‐ and cross pollen.
• We recorded full self‐sterility for C. contractus and C. ventricosus, and partial self‐sterility for C. mackenii. In C. contractus, we found no differences in the growth rates of self‐ and cross‐pollen tubes, nor in the proportions of ovules penetrated by self‐ and cross‐pollen tubes. In this species, seed set was depressed (relative to cross‐pollinated controls) when flowers received a mixture of self and cross pollen, but this was not the case for C. mackenii.
• These results reveal variation in breeding systems among Cyrtanthus species and highlight the potential for gender conflict in self‐sterile species in which ovules are penetrated and disabled by pollen tubes from self pollen.

     

A dual gene‐silencing vector system for monocot and dicot plants

Plant virus‐based gene‐silencing vectors have been extensively and successfully used to elucidate functional genomics in plants. However, only limited virus‐induced gene‐silencing (VIGS) vectors can be used in both monocot and dicot plants. Here, we established a dual gene‐silencing vector system based on Bamboo mosaic virus (BaMV) and its satellite RNA (satBaMV). Both BaMV and satBaMV vectors could effectively silence endogenous genes in Nicotiana benthamiana and Brachypodium distachyon. The satBaMV vector could also silence the green fluorescent protein (GFP) transgene in GFP transgenic N. benthamiana. GFP transgenic plants co‐agro‐inoculated with BaMV and satBaMV vectors carrying sulphur and GFP genes, respectively, could simultaneously silence both genes. Moreover, the silenced plants could still survive with the silencing of genes essential for plant development such as heat‐shock protein 90 (Hsp90) and Hsp70. In addition, the satBaMV‐ but not BaMV‐based vector could enhance gene‐silencing efficiency in newly emerging leaves of N. benthamiana deficient in RNA‐dependant RNA polymerase 6. The dual gene‐silencing vector system of BaMV and satBaMV provides a novel tool for comparative functional studies in monocot and dicot plants.     

Two combinatorial patterns of telomere histone marks in plants with canonical and non‐canonical telomere repeats

Telomeres, nucleoprotein structures at the ends of linear eukaryotic chromosomes, are crucial for the maintenance of genome integrity. In most plants, telomeres consist of conserved tandem repeat units comprising the TTTAGGG motif. Recently, non‐canonical telomeres were described in several plants and plant taxons, including the carnivorous plant Genlisea hispidula (TTCAGG/TTTCAGG), the genus Cestrum (Solanaceae; TTTTTTAGGG), and plants from the Asparagales order with either a vertebrate‐type telomere repeat TTAGGG or Allium genus‐specific CTCGGTTATGGG repeat. We analyzed epigenetic modifications of telomeric histones in plants with canonical and non‐canonical telomeres, and further in telomeric chromatin captured from leaves of Nicotiana benthamiana transiently transformed by telomere CRISPR‐dCas9‐eGFP, and of Arabidopsis thaliana stably transformed with TALE_telo C‐3×GFP. Two combinatorial patterns of telomeric histone modifications were identified: (i) an Arabidopsis‐like pattern (A. thaliana, G. hispidula, Genlisea nigrocaulis, Allium cepa, Narcissus pseudonarcissus, Petunia hybrida, Solanum tuberosum, Solanum lycopersicum) with telomeric histones decorated predominantly by H3K9me2; (ii) a tobacco‐like pattern (Nicotiana tabacum, N. benthamiana, C. elegans) with a strong H3K27me3 signal. Our data suggest that epigenetic modifications of plant telomere‐associated histones are related neither to the sequence of the telomere motif nor to the lengths of the telomeres. Nor the phylogenetic position of the species plays the role; representatives of the Solanaceae family are included in both groups. As both patterns of histone marks are compatible with fully functional telomeres in respective plants, we conclude that the described specific differences in histone marks are not critical for telomere functions.     

Expression of ovule and integument‐associated genes in reduced ovules of Santalales

SUMMARY Santalales comprise mainly parasitic plants including mistletoes and sandalwoods. Bitegmic ovules similar to those found in most other angiosperms are seen in many members of the order, but other members exhibit evolutionary reductions to the unitegmic and ategmic conditions. In some mistletoes, extreme reduction has resulted in the absence of emergent ovules such that embryo sacs appear to remain embedded in placental tissues. Three santalalean representatives (Comandra, Santalum, and Phoradendron), displaying unitegmic, and ategmic ovules, were studied. Observed ovule morphologies were consistent with published reports, including Phoradendron serotinum, which we interpret as having reduced ategmic ovules, consistent with earlier reports on this species. For further understanding of the nature of the ovule reductions we isolated orthologs of the Arabidopsis genes AINTEGUMENTA (ANT) and BELL1 (BEL1), which are associated with ovule development in this species. We observed ovular expression of ANT and BEL1 in patterns largely resembling those seen in the integumented ovules of Arabidopsis. These genes were found to be expressed in the integument of unitegmic ovules and in the surface layers of ategmic ovules, and in some cases, expression of BEL1 was also observed in the surrounding carpel tissue. We hypothesize that ategmic ovules derive from a fusion of the integuments with the nucellus or that the nucellus has taken on some of the characteristics confined to integuments in ancestral species.     

In‐depth characterization of Trichoderma reesei cellobiohydrolase TrCel7A produced in Nicotiana benthamiana reveals limitations of cellulase production in plants by host‐specific post‐translational modifications

Sustainable production of biofuels from lignocellulose feedstocks depends on cheap enzymes for degradation of such biomass. Plants offer a safe and cost‐effective production platform for biopharmaceuticals, vaccines and industrial enzymes boosting biomass conversion to biofuels. Production of intact and functional protein is a prerequisite for large‐scale protein production, and extensive host‐specific post‐translational modifications (PTMs) often affect the catalytic properties and stability of recombinant enzymes. Here we investigated the impact of plant PTMs on enzyme performance and stability of the major cellobiohydrolase TrCel7A from Trichoderma reesei, an industrially relevant enzyme. TrCel7A was produced in Nicotiana benthamiana using a vacuum‐based transient expression technology, and this recombinant enzyme (TrCel7A^rec) was compared with the native fungal enzyme (TrCel7A^nat) in terms of PTMs and catalytic activity on commercial and industrial substrates. We show that the N‐terminal glutamate of TrCel7A^rec was correctly processed by N. benthamiana to a pyroglutamate, critical for protein structure, while the linker region of TrCel7A^rec was vulnerable to proteolytic digestion during protein production due to the absence of O‐mannosylation in the plant host as compared with the native protein. In general, the purified full‐length TrCel7A^rec had 25% lower catalytic activity than TrCel7A^nat and impaired substrate‐binding properties, which can be attributed to larger N‐glycans and lack of O‐glycans in TrCel7A^rec. All in all, our study reveals that the glycosylation machinery of N. benthamiana needs tailoring to optimize the production of efficient cellulases.     

Beta‐globin gene evolution in the ruminants: evidence for an ancient origin of sheep haplotype B

Domestic sheep (Ovis aries) can be divided into two groups with significantly different responses to hypoxic environments, determined by two allelic beta‐globin haplotypes. Haplotype A is very similar to the goat beta‐globin locus, whereas haplotype B has a deletion spanning four globin genes, including beta‐C globin, which encodes a globin with high oxygen affinity. We surveyed the beta‐globin locus using resequencing data from 70 domestic sheep from 42 worldwide breeds and three Ovis canadensis and two Ovis dalli individuals. Haplotype B has an allele frequency of 71.4% in O. aries and was homozygous (BB) in all five wild sheep. This shared ancestry indicates haplotype B is at least 2–3 million years old. Approximately 40 kb of the sequence flanking the ~37‐kb haplotype B deletion had unexpectedly low identity between haplotypes A and B. Phylogenetic analysis showed that the divergent region of sheep haplotype B is remarkably distinct from the beta‐globin loci in goat and cattle but still groups with the Ruminantia. We hypothesize that this divergent ~40‐kb region in haplotype B may be from an unknown ancestral ruminant and was maintained in the lineage to O. aries, but not other Bovidae, evolving independently of haplotype A. Alternatively, the ~40‐kb sequence in haplotype B was more recently acquired by an ancestor of sheep from an unknown non‐Bovidae ruminant, replacing part of haplotype A. Haplotype B has a lower nucleotide diversity than does haplotype A, suggesting a recent bottleneck, whereas the higher frequency of haplotype B suggests a subsequent spread through the global population of O. aries.     

Glucosylation of the phytoalexin N‐feruloyl tyramine modulates the levels of pathogen‐responsive metabolites in Nicotiana benthamiana

Enzyme promiscuity, a common property of many uridine diphosphate sugar‐dependent glycosyltransferases (UGTs) that convert small molecules, significantly hinders the identification of natural substrates and therefore the characterization of the physiological role of enzymes. In this paper we present a simple but effective strategy to identify endogenous substrates of plant UGTs using LC‐MS‐guided targeted glycoside analysis of transgenic plants. We successfully identified natural substrates of two promiscuous Nicotiana benthamiana UGTs (NbUGT73A24 and NbUGT73A25), orthologues of pathogen‐induced tobacco UGT (TOGT) from Nicotiana tabacum, which is involved in the hypersensitive reaction. While in N. tabacum, TOGT glucosylated scopoletin after treatment with salicylate, fungal elicitors and the tobacco mosaic virus, NbUGT73A24 and NbUGT73A25 produced glucosides of phytoalexin N‐feruloyl tyramine, which may strengthen cell walls to prevent the intrusion of pathogens, and flavonols after agroinfiltration of the corresponding genes in N. benthamiana. Enzymatic glucosylation of fractions of a physiological aglycone library confirmed the biological substrates of UGTs. In addition, overexpression of both genes in N. benthamiana produced clear lesions on the leaves and led to a significantly reduced content of pathogen‐induced plant metabolites such as phenylalanine and tryptophan. Our results revealed some additional biological functions of TOGT enzymes and indicated a multifunctional role of UGTs in plant resistance.     

Dissecting virulence function from recognition: cell death suppression in Nicotiana benthamiana by XopQ/HopQ1‐family effectors relies on EDS1‐dependent immunity

Many Gram‐negative plant pathogenic bacteria express effector proteins of the XopQ/HopQ1 family which are translocated into plant cells via the type III secretion system during infection. In Nicotiana benthamiana, recognition of XopQ/HopQ1 proteins induces an effector‐triggered immunity (ETI) reaction which is not associated with strong cell death but renders plants immune against Pseudomonas syringae and Xanthomonas campestris pv. vesicatoria strains. Additionally, XopQ suppresses cell death in N. benthamiana when transiently co‐expressed with cell death inducers. Here, we show that representative XopQ/HopQ1 proteins are recognized similarly, likely by a single resistance protein of the TIR‐NB‐LRR class. Extensive analysis of XopQ derivatives indicates the recognition of structural features. We performed Agrobacterium‐mediated protein expression experiments in wild‐type and EDS1‐deficient (eds1) N. benthamiana leaves, not recognizing XopQ/HopQ1. XopQ recognition limits multiplication of Agrobacterium and attenuates levels of transiently expressed proteins. Remarkably, XopQ fails to suppress cell death reactions induced by different effectors in eds1 plants. We conclude that XopQ‐mediated cell death suppression in N. benthamiana is due to the attenuation of Agrobacterium‐mediated protein expression rather than the cause of the genuine XopQ virulence activity. Thus, our study expands our understanding of XopQ recognition and function, and also challenges the commonly used co‐expression assays for elucidation of in planta effector activities, at least under conditions of ETI induction.     

Arabidopsis PLC2 is involved in auxin‐modulated reproductive development

Phospholipase C (PLC) is an enzyme that plays crucial roles in various signal transduction pathways in mammalian cells. However, the role of PLC in plant development is poorly understood. Here we report involvement of PLC2 in auxin‐mediated reproductive development in Arabidopsis. Disruption of PLC2 led to sterility, indicating a significant role for PLC2 in reproductive development. Development of both male and female gametophytes was severely perturbed in plc2 mutants. Moreover, elevated auxin levels were observed in plc2 floral tissues, suggesting that the infertility of plc2 plants may be associated with increased auxin concentrations in the reproductive organs. We show that expression levels of the auxin reporters DR5:GUS and DR5:GFP were elevated in plc2 anthers and ovules. In addition, we found that expression of the auxin biosynthetic YUCCA genes was increased in plc2 plants. We conclude that PLC2 is involved in auxin biosynthesis and signaling, thus modulating development of both male and female gametophytes in Arabidopsis.     

Characterization of <Emphasis Type="Italic">HoMADS 1</Emphasis> and its induction by plant hormones during <Emphasis Type="Italic">in vitro</Emphasis> ovule development in <Emphasis Type="Italic">Hyacinthus orientalis</Emphasis> L.

To understand the molecular mechanism of ovule development, a MADS box gene,HoMADS 1, has been isolated from the ovule tissues of Hyacinthus. Sequence comparison showed that HoMADS 1 is highly homologous to both class C and D genes. Furthermore, phylogenetic analysis suggests that HoMADS 1 is most likely a class D MADS box gene. RNA hybridization revealed that HoMADS 1 was exclusively expressed in the ovules. Over-expressing HoMADS 1 in transgenic Arabidopsis plants produced ectopic carpelloid structures, including ovules, indicating that HoMADS 1 is involved in the determination of carpel and ovule identities. Interestingly, during in vitro flowering, no HoMADS 1 mRNA was detected in the floral tissues at high level hormones in the media. However, HoMADS 1 mRNA accumulated in the floral tissues when the regenerated flowers were transferred to the media containing low level hormones which could induce in vitro ovule formation. Our data suggest that the induction of HoMADS 1 by plant hormones may play important roles during ovule initiation and development in the regenerated flower. Whether HoMADS 1 expression is also regulated by cytokinin and auxin during ovule development in planta remains to be investigated.     

The NIa‐Pro protein of Turnip mosaic virus improves growth and reproduction of the aphid vector,Myzus persicae (green peach aphid)

Many plant viruses depend on aphids and other phloem‐feeding insects for transmission within and among host plants. Thus, viruses may promote their own transmission by manipulating plant physiology to attract aphids and increase aphid reproduction. Consistent with this hypothesis, Myzus persicae (green peach aphids) prefer to settle on Nicotiana benthamiana infected with Turnip mosaic virus (TuMV) and fecundity on virus‐infected N. benthamiana and Arabidopsis thaliana (Arabidopsis) is higher than on uninfected controls. TuMV infection suppresses callose deposition, an important plant defense, and increases the amount of free amino acids, the major source of nitrogen for aphids. To investigate the underlying molecular mechanisms of this phenomenon, 10 TuMV genes were over‐expressed in plants to determine their effects on aphid reproduction. Production of a single TuMV protein, nuclear inclusion a‐protease domain (NIa‐Pro), increased M. persicae reproduction on both N. benthamiana and Arabidopsis. Similar to the effects that are observed during TuMV infection, NIa‐Pro expression alone increased aphid arrestment, suppressed callose deposition and increased the abundance of free amino acids. Together, these results suggest a function for the TuMV NIa‐Pro protein in manipulating the physiology of host plants. By attracting aphid vectors and promoting their reproduction, TuMV may influence plant–aphid interactions to promote its own transmission.