Modern tomato cultivation techniques: Plant-virus interactions make tomatoes acquire resistance
First, the impact of abiotic stress
Environmental pressures affect global crop production. Drought and high temperatures are the most severe abiotic stresses, especially in countries with hot climates. In addition, they increase the stress on insects, which pose an additional threat due to viruses carried by insect vectors. For a long time, viruses were exclusively considered pathogens that cause damage to plants, using host resources and compounds to reproduce themselves.
In recent years, however, new information has described the beneficial effects of some viruses on their plant hosts. Viruses are defined as interactions with plant cellular mechanisms that protect plants from some abiotic stresses.
A groundbreaking study in this area describes the ability of RNA viruses such as bromomosaic virus (BMV), tobacco mosaic virus (TMV), and tobacco rattle virus (TRV) to improve drought tolerance in host plants, while cucumber mosaic virus (CMV) induces plant resistance not only to drought but also to cold. Infected tissues are characterized by increased levels of osmoprotectants and antioxidants. Infection with potato virus X (PVX) and plumpox virus (PPV) further improved drought tolerance. Although PVX or PPV-induced improvements in plant survival under drought were not described in detail, increased levels of salicylic acid (SA) rather than abscisic acid (ABA) were found in infected plants.
These results were unexpected because ABA is a key hormone that regulates the plant's response to drought, while SA is induced in response to pathogen infection. However, the establishment of drought tolerance in an ABA-independent manner was also shown in transgenic Arabidopsis thaliana expressing the tomato yellow leaf curl C4 gene or the radish mosaic virus (TuMV) 6K2 gene. TRV has been shown to promote plant tolerance to low temperatures, and PVX tolerance to environmental oxidation.
2. Recent progressive research
Nematode viruses are small round ssDNA (cssDNA) viruses. Tomato yellow leaf curl virus (TYLCV) is a typical ovale virus that infects tomato plants. The TYLCV virus encapsulates a single cssDNA molecule (monomer) of about 2800 nucleotides. Until recently, it was thought that the single-part TYLCV genome encodes six genes: a viral strand with two genes, V1 (cortical protein CP) and V2, and a complementary strand with four genes, C1 through C4.
However, recent bioinformatics studies have contributed to the discovery of six additional TYLCV open reading frameworks that code for proteins with fewer than 80 amino acids, some of which show specific subcellular localization. For example, V3, expressed during viral infection, is localized in a Golgi apparatus as an RNA silencing inhibitor and transmitted along the microfilaments to the plasma to facilitate viral cell-to-cell movement.
Another TYLCV protein, created C5, is a pathogenic determinant and RNA silencing inhibitor. Another recent study showed that by screening the translation starting point of the two-part tomato leaf curly Thai virus, potential viral proteins encoded by the A and B genomes were discovered and the translation of different protein isoforms located in various cell compartments was found to be important.
TYLCV spreads between plants in a cyclical and persistent manner through its insect vector, the white fly Bemisia tabaci, which feeds on more than 600 plant species worldwide. In commercial tomatoes, yield losses can reach 100%. The threat of TYLCV pathogenicity has decreased with the development of tomato lines and varieties that are resistant to TYLCV, first in Israel and later after infection in many other countries, these tolerant tomatoes (in this case, R-TYLCV) do not significantly change their morphological characteristics and exhibit normal growth and yield, even in the case of mass inoculation of viral white flies. After long-term infection, the viral load of R-TYLCV tomatoes is comparable to that in TYLCV-susceptible tomatoes (S-TYLCV), while retaining their agronomic properties.
III. Results
In whitefly-mediated infection of S-TYLCV tomato plants, TYLCV does not induce hypersensitivity and cell death until the diseased tomatoes age. Conversely, TYLCV's ability to improve the survival of infected tomatoes (S and R) exposed to different pressures has been gradually discovered.
Tomato cultivation is threatened by environmental stress (e.g. heat, drought) and viral infections (mainly belonging to the tomato yellow leaf curly virus family - TYLCVs). Unlike many RNA viruses, TYLCV infection does not induce hypersensitivity and cell death in tomato plants. To ensure successful infection, TYLCV retains a suitable cellular environment in which it can multiply.
Infected plants experience mild stress, undergo adaptation, and are partially "ready" to be exposed to other environmental stressors. Plant wilt and growth cessation caused by heat and drought were inhibited by TYLCV infection, mainly by downregulating the heat shock transcription factors HSFA1, HSFA2 and HSFB1, thereby inhibiting the expression of HSF-regulated stress genes. In particular, TYLCV alleviates the acute stress response by inducing protein complexes and aggregates to capture HSFA2, which would otherwise lead to plant death. Viral infections can alleviate stress-induced increases in metabolites such as carbohydrates and amino acids and lead to their redistribution from buds to roots. In the case of high temperature and lack of water, TYLCV induces plant cell homeostasis, promoting host survival. Therefore, this virus-plant interaction is beneficial for both parties.
