雅思阅读 36: Reinventing the Tomato（重塑番茄）

改编自 Plant Breeding and Biotechnology / PMC 综述（2026年）。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://pmc.ncbi.nlm.nih.gov/articles/PMC12607859/

Reading Passage

A. For most of the twentieth century, plant breeders were celebrated for squeezing more kilograms of grain and fruit out of every hectare. The "Green Revolution" of the 1960s and 1970s is credited with feeding billions, and it did so by relentlessly selecting for yield. That emphasis came at a cost. The varieties that won the most attention were often selected for long shelf life, uniformity and transportability rather than flavour or nutrition, and consumers learned to accept tomatoes that looked flawless on the supermarket shelf but tasted of little once bitten into. Improving any single quality the traditional way was also painfully slow: crossing two plants, then growing the offspring and crossing them back to the desirable parent through many generations to retain the trait without losing everything else good about the variety, could take a decade or more. Worse, unwanted genes from the wild relative inevitably arrived along with the useful one — a problem breeders call "linkage drag", which no amount of patience fully removes. A set of new molecular tools has, in the last few years, begun to change that bargain.

B. The tool in question is CRISPR-Cas9, a precision editing system borrowed from a bacterial defence mechanism that bacteria use to snip apart invading viruses. In the laboratory, a short piece of guide RNA leads the Cas9 enzyme to a specific spot on a chromosome, where the enzyme acts as a pair of molecular scissors. Where older genetic engineering inserted foreign DNA at random, CRISPR allows a researcher to cut a plant's own genome at a chosen spot, disabling a particular gene or altering how strongly it is switched on. Crucially, the resulting plant need not contain any leftover foreign genetic material; once the edit is made, the editing machinery can simply be bred away in the next generation, leaving a crop that differs from its parent only by the targeted change. The speed is striking. A trait that once demanded ten years of crossing can now be introduced in roughly three, and the "drag" of unwanted linked genes is largely sidestepped. The precision also means breeders can alter a single quality without disturbing the rest of a variety's character — a prized tomato need no longer be rebuilt from scratch. Tomatoes, short-lived, easy to grow and rich in genes already well mapped, have become the proving ground for the method.

C. Researchers have aimed their edits not at bigger fruit but at better food. Disabling genes that normally break down a calming compound called GABA has raised its concentration in the flesh several-fold, and consumers in Japan can already buy tomatoes enriched in this way; other edits have lifted vitamin C, the red pigment lycopene and even the mood-related molecule serotonin, normally absent from ripe fruit. The most striking experiment re-imagined the tomato as a source of vitamin D. By switching off a single gene that converts a precursor into cholesterol, scientists let that precursor accumulate in the leaves and fruit; when the tissue is exposed to ultraviolet light, it converts naturally into vitamin D3 — offering a plant-based answer to a deficiency that affects more than a billion people worldwide, particularly those living at higher latitudes. None of these plants carries genes from another species, which is precisely what sets them apart from the genetically modified crops of the 1990s and why regulators in several countries treat them more leniently.

D. Nutrition is only half the story. The same cuts can reshape the whole plant. Edits to genes governing growth produce compact, bushy varieties whose fruits ripen almost simultaneously, suiting mechanical harvest that would otherwise pick unripe tomatoes along with ripe ones; other edits confer tolerance to salt, drought and heat, valuable traits as arable land becomes drier and warmer, or resistance to diseases such as bacterial spot that currently force growers to spray repeatedly. A longer, firmer shelf life reduces the waste that happens after the fruit leaves the farm and sits in a lorry or a supermarket shelf for days on end, a particular concern for growers who sell over long distances. The approach has even been turned on neglected wild species. A cousin of the tomato called the groundcherry, never fully domesticated because its fruits drop to the ground the moment they ripen and its bushes sprawl untidily, has been coaxed in a handful of edits into a compact plant that holds its fruit and ripens in step — an almost instant form of domestication that previously would have taken human farmers thousands of years.

E. Whether such crops reach shop shelves depends less on the science than on the rules that govern them. Because CRISPR can make a tiny, targeted change without adding foreign DNA, many countries now treat gene-edited crops differently from the older, controversial transgenic plants whose genes came from entirely unrelated organisms, such as bacteria. The United States, Britain and Japan have largely exempted edits indistinguishable from natural mutations from lengthy approval, treating them as equivalent to conventionally bred varieties, while the European Union has taken a more cautious, case-by-case path that imposes stricter labelling and longer assessments. Public suspicion, inherited from the decades-long debate over genetically modified food, has not vanished, and labels and acceptance vary widely between markets, with some shoppers ready to buy a vitamin-D-enriched tomato and others wary of anything that touches a plant's genes. The technology, in other words, has outrun neither its regulations nor the public's trust — but the tomato, once a symbol of flavour sacrificed to shelf life and long-distance transport, may yet become the first crop to be improved, deliberately and quickly, for what it does inside the body rather than for how long it survives the lorry.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. A precise tool that leaves no foreign DNA behind ii. Why twentieth-century tomatoes lost their taste iii. Editing the fruit itself to make it more nutritious iv. Reshaping the whole plant and reviving forgotten crops v. How CRISPR causes disease in wild species vi. Regulation and public acceptance — the real bottleneck vii. The history of tomato cultivation in Europe

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. What problem does the writer identify with traditional breeding? A. It produced fruit that was too small. B. It was slow and brought unwanted genes alongside useful ones. C. It made all tomatoes taste identical. D. It could only be applied to wheat.

6. What is distinctive about a CRISPR-edited crop? A. It always contains bacterial DNA. B. It can carry a targeted change while containing no foreign genes. C. It grows twice as tall as conventional crops. D. It is immune to all plant diseases.

7. How did researchers create a vitamin-D-rich tomato? A. By spraying the fruit with synthetic vitamin D. B. By feeding it on a special mineral fertiliser. C. By letting a precursor accumulate that converts under UV light. D. By grafting it onto a mushroom.

8. What is said about the groundcherry? A. It was domesticated thousands of years ago. B. It has been turned into a compact, fruit-holding plant through a few edits. C. It cannot be grown outside the tropics. D. It is a variety of potato.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. Traditional breeding could take around ten years to introduce a trait.
10. CRISPR-edited tomatoes always contain foreign genes from bacteria.
11. GABA levels in edited tomatoes have been increased several-fold.
12. Every country now has identical rules for gene-edited crops.
13. The vitamin D3 tomato was developed by a team in Japan.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

Rather than inserting foreign DNA at random, CRISPR cuts a plant's own genome at a chosen spot. After the edit, the editing machinery can be bred away, leaving a plant with no leftover (14) __________ material. The speed is striking: a trait once taking ten years now needs about three, and the old problem of unwanted linked genes, or linkage (15) __________, is largely avoided.

答案与解析

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