Virus-Infected Melon Plants Emit Volatiles that Induce Gene Deregulation in Neighboring Healthy Plants

It is well described that viral infections stimulate the emission of plant volatiles able to recruit viral vectors thereby promoting virus spread. In contrast, much less is known on the effects that emitted volatiles may have on the metabolism of healthy neighboring plants, which are potential targets for new infections through vector transmission. Watermelon mosaic virus (WMV) (genus Potyvirus, family Potyviridae) is an aphid-transmitted virus endemic in cucurbit crops worldwide. We have compared gene expression profiles of WMV-infected melon plants with those of healthy or healthy-but-cohabited-with-infected plants. Pathogenesis-related (PR) and small heat shock protein encoding genes were deregulated in cohabited plants, and PR deregulation depended on the distance to the infected plant. The signaling was short distance in the experimental conditions used, and cohabiting had a moderate effect on the plant susceptibility to WMV. Static headspace experiments showed that benzaldehyde and γ-butyrolactone were significantly over-emitted by WMV-infected plants. Altogether, our data suggest that perception of a volatile signal encoded by WMV-infected tissues triggers a response to prepare healthy tissues or/and healthy neighboring plants for the incoming infections.

Differential expression of IDA (INFLORESCENCE DEFICIENT IN ABSCISSION)-like genes in Nicotiana benthamiana during corolla abscission, stem growth and water stress

BACKGROUND

IDA (INFLORESCENCE DEFICIENT IN ABSCISSION)-like signaling peptides and the associated HAE (HAESA)-like family of receptor kinases were originally reported in the model plant Arabidopsis thaliana (Arabidopsis) to be deeply involved in the regulation of abscission. Actually, IDA peptides, as cell-to-cell communication elements, appear to be implicated in many developmental processes that rely on cell separation events, and even in the responses to abiotic stresses. However, the knowledge related to the molecular machinery regulating abscission in economically important crops is scarce. In this work, we determined the conservation and phylogeny of the IDA-like and HAE-like gene families in relevant species of the Solanaceae family and analyzed the expression of these genes in the allopolyploid Nicotiana benthamiana, in order to identify members involved in abscission, stem growth and in the response to drought conditions.

RESULTS

The phylogenetic relationships among the IDA-like members of the Solanaceae studied, grouped the two pairs of NbenIDA1 and NbenIDA2 protein homeologs with the Arabidopsis prepropeptides related to abscission. Analysis of promoter regions searching for regulatory elements showed that these two pairs of homeologs contained both hormonal and drought response elements, although NbenIDA2A lacked the hormonal regulatory elements. Expression analyses showed that the pair of NbenIDA1 homeologs were upregulated during corolla abscission. NbenIDA1 and NbenIDA2 pairs showed tissue differential expression under water stress conditions, since NbenIDA1 homeologs were highly expressed in stressed leaves while NbenIDA2 homeologs, especially NbenIDA2B, were highly expressed in stressed roots. In non-stressed active growing plants, nodes and internodes were the tissues with the highest expression levels of all members of the IDA-like family and their putative HAE-like receptors.

CONCLUSION

Our results suggest that the pair of NbenIDA1 homeologs are involved in the natural process of corolla abscission while both pairs of NbenIDA1 and NbenIDA2 homeologs are implicated in the response to water stress. The data also suggest that IDA peptides may be important during stem growth and development. These results provide additional evidence that the functional module formed by IDA peptides and its receptor kinases, as defined in Arabidopsis, may also be conserved in Solanaceae.

Differential expression of IDA (INFLORESCENCE DEFICIENT IN ABSCISSION)-like genes in Nicotiana benthamiana during corolla abscission, stem growth and water stress

BACKGROUND

IDA (INFLORESCENCE DEFICIENT IN ABSCISSION)-like signaling peptides and the associated HAE (HAESA)-like family of receptor kinases were originally reported in the model plant Arabidopsis thaliana (Arabidopsis) to be deeply involved in the regulation of abscission. Actually, IDA peptides, as cell-to-cell communication elements, appear to be implicated in many developmental processes that rely on cell separation events, and even in the responses to abiotic stresses. However, the knowledge related to the molecular machinery regulating abscission in economically important crops is scarce. In this work, we determined the conservation and phylogeny of the IDA-like and HAE-like gene families in relevant species of the Solanaceae family and analyzed the expression of these genes in the allopolyploid Nicotiana benthamiana, in order to identify members involved in abscission, stem growth and in the response to drought conditions.

RESULTS

The phylogenetic relationships among the IDA-like members of the Solanaceae studied, grouped the two pairs of NbenIDA1 and NbenIDA2 protein homeologs with the Arabidopsis prepropeptides related to abscission. Analysis of promoter regions searching for regulatory elements showed that these two pairs of homeologs contained both hormonal and drought response elements, although NbenIDA2A lacked the hormonal regulatory elements. Expression analyses showed that the pair of NbenIDA1 homeologs were upregulated during corolla abscission. NbenIDA1 and NbenIDA2 pairs showed tissue differential expression under water stress conditions, since NbenIDA1 homeologs were highly expressed in stressed leaves while NbenIDA2 homeologs, especially NbenIDA2B, were highly expressed in stressed roots. In non-stressed active growing plants, nodes and internodes were the tissues with the highest expression levels of all members of the IDA-like family and their putative HAE-like receptors.

CONCLUSION

Our results suggest that the pair of NbenIDA1 homeologs are involved in the natural process of corolla abscission while both pairs of NbenIDA1 and NbenIDA2 homeologs are implicated in the response to water stress. The data also suggest that IDA peptides may be important during stem growth and development. These results provide additional evidence that the functional module formed by IDA peptides and its receptor kinases, as defined in Arabidopsis, may also be conserved in Solanaceae.

Mechanism of plant eIF4E-mediated resistance against a Carmovirus (Tombusviridae): cap-independent translation of a viral RNA controlled in cis by an (a)virulence determinant

Translation initiation factors are universal determinants of plant susceptibility to RNA viruses, but the underlying mechanisms are poorly understood. Here, we show that a sequence in the 3' untranslated region (3'-UTR) of a viral genome that is responsible for overcoming plant eIF4E-mediated resistance (virulence determinant) functions as a 3' cap-independent translational enhancer (3'-CITE). The virus/plant pair studied here is Melon necrotic spot virus (MNSV) and melon, for which a recessive resistance controlled by melon eIF4E was previously described. Chimeric viruses between virulent and avirulent isolates enabled us to map the virulence and avirulence determinants to 49 and 26 nucleotides, respectively. The translational efficiency of a luc reporter gene flanked by 5'- and 3'-UTRs from virulent, avirulent and chimeric viruses was analysed in vitro, in wheatgerm extract, and in vivo, in melon protoplasts, showing that: (i) the virulence determinant mediates the efficient cap-independent translation in vitro and in vivo; (ii) the avirulence determinant was able to promote efficient cap-independent translation in vitro, but only when eIF4E from susceptible melon was added in trans, and, coherently, only in protoplasts of susceptible melon, but not in the protoplasts of resistant melon; (iii) these activities required the 5'-UTR of MNSV in cis. Thus, the virulence and avirulence determinants function as 3'-CITEs. The activity of these 3'-CITEs was host specific, suggesting that an inefficient interaction between the viral 3'-CITE of the avirulent isolate and eIF4E of resistant melon impedes the correct formation of the translation initiation complex at the viral RNA ends, thereby leading to resistance.