Author: Théophile Niyitegeka

Tomatoes have come a long way from their origins as pea-sized berries due to humans breeding tomato plants to produce bigger fruit. However, favorable mutations that went along with increased fruit size and other beneficial traits do not always play well together. A study published in Cell on May 18 found that natural mutations in two important tomato genes that were selected for different purposes in breeding can cause extreme branching and reduce fruit yield when they occur in the same plant. However, the researchers have found a way to use those genes to create an improved tomato plant that grows a larger number of tomatoes.

One of the two genes is ancient, dating back to when Native Americans in South and Central America domesticated the tomato plant more than 8,000 years ago. That gene causes the green leafy “cap” on top of tomato fruits to grow larger, the researchers found. The other gene, called Jointless2, is a 20th-century mutant, which results in a smoother stem connected to the fruit and a firmer attachment to the plant. Jointless2 is particularly sought after because it makes tomatoes easier to harvest, but the presence of both mutations in one plant causes the branches that make the flowers (and later, fruit) — known botanically as “inflorescences” — to branch wildly into patterns that look “a bit like a broom.”

“On the surface, you would think that’s great because more branches on each infloresence means more flowers, which would mean more fruits; but in fact, more branches and flowers doesn’t always translate to more fruits,” says senior author Zachary Lippman, a plant geneticist at Cold Spring Harbor Laboratory. “In order to make those fruits, the plant has to pump a lot of resources into the young fruits as they start to grow. But plant can’t handle that imbalance of having too many fruits, so the fertility is quite low.” In other words, highly branched tomato plants end up producing fewer tomatoes.

However, Lippman and his colleagues thought that there might be advantages to having low levels of branching, such that the “weak branching” plant would have more flowers than a non-branching plant but not so many that the tomatoes fail to grow. They decided to investigate the genes behind flower-bearing branches and their growth patterns.

First, the team discovered genes that caused “strong branching” mutants. They found mutations in two closely related genes, both of which play a role in initiating flower growth by turning genes on and off in plant stem cells. One of the genes, Jointless2, was already well known in tomato genetics circles, but the second gene’s function was unknown. To find out what the gene did without Jointless2 around, the researchers used CRISPR “gene editing” to create a tomato with a mutation in the mystery gene. Those mutants grew larger sepals, the small leaves at the base of a flower that become a part of the little green cap on the fruits. It’s unclear what the benefit of larger sepals and a larger green cap would be, Lippman says, but the mutation is present in more than 85% of modern tomatoes, meaning that it’s hard to breed a jointless tomato without running the risk of extreme branching.

“In the 1970s, breeders wanted to use Jointless2 so much that they said, ‘We’re going to find a way to use the genetics to our advantage, and we’re going to find other genes to suppress the branching.’ So they knew they had this extreme branching, but they didn’t know which gene was mutated,” says Lippman. “Their goal was to suppress the branching, to bring it back to the unbranched state, which is what you see in the grocery store with tomatoes on the vine. And they achieved it. They achieved it in many cases, but not all. In so doing, we feel that they have missed an opportunity to achieve weak branching, to tune the architecture in such a way that you can get a benefit.”

With the newly identified branch-driving genes in hand, the researchers were able to use natural mutations and CRISPR to engineer several different tomato plants with varying degrees of inflorescence branching, including one with “weak branching” but high fruit yield. Lippman hopes that the results from this study can be useful not only for tomato breeders, but for other crops, as well. Tomatoes are in the same genus as potatoes and eggplants (as well as poisonous Nightshades). They are also in the same family as tobacco and bell peppers. Some of these genes may also be important for those crops, and the principles behind the experiment may be applicable to distantly related plants, too.

“The more we understand about basic plant biology, basic mechanisms of plant growth, and plant development, the more we have at our fingertips the knowledge and tools to rework the system or tune the system and exploit the system,” says Lippman. “Even when we find negative mutations, we can exploit that knowledge and turn them into a positive.”

Source:Science Daily

Among the hundreds of species of damselfish, only a few protect and care for their young; a newly discovered species raises the number from three to four

The vast majority of coral reef fish produce large numbers of young that disperse into the ocean as larvae, drifting with the currents before settling down on a reef. Giacomo Bernardi, a professor of ecology and evolutionary biology at UC Santa Cruz, studies reef fish that buck this trend and keep their broods on the reef, protecting the young until they are big enough to fend for themselves.

On a recent trip to the Philippines, Bernardi and his graduate students discovered a new species of damselfish that exhibits this unusual parental care behavior. Out of about 380 species of damselfish, only three brood-guarding species were known prior to this discovery. Bernardi’s team had gone to the Philippines to study two of them, both in the genus Altrichthys, that live in shallow water off the small island of Busuanga. On the last day of the trip, the researchers went snorkeling in a remote area on the other side of the island from their study site.

“Immediately, as soon as we went in the water, we saw that this was a different species,” Bernardi said. “It’s very unusual to see a coral reef fish guarding its babies, so it’s really cool when you see it.”

Genetic tests on the specimens they collected confirmed that it is a new species, which the researchers named Altrichthys alelia (Alelia’s damselfish, derived from the names of Bernardi’s children, Alessio and Amalia, who helped with his field research). A paper on the new species was published May 18 in the journal ZooKeys.

Parental care dramatically improves the chances of survival for the offspring. According to Bernardi, less than one percent of larvae that disperse into the ocean survive to settle back on a reef, whereas survival rates can be as high as 35 percent for the offspring of the Altrichthys species. Yet the parental care strategy remains rare among reef fish.

“It’s a huge fitness advantage, so why don’t they all do that? There must also be a huge disadvantage,” Bernardi said.

One big disadvantage is that the young are unable to colonize new sites far from the home reef of their parents. As a result, brood-guarding species (the technical term is “apelagic” species, because they don’t have a pelagic, ocean-going phase) tend to occur in highly restricted areas, which leaves them more vulnerable to extinction.

“I suspect that species evolve this strategy regularly, and they are successful until there is some change to the local habitat, and then the whole population gets wiped out,” Bernardi said. “These are very fragile species. The Banggai cardinalfish is one that was discovered just a few years ago in a small area in Indonesia, and it’s already on the endangered species list.”

Source:Science Daily

New research from scientists at the Howard Hughes Medical Institute’s Janelia Research Campus shows that distant parts of the brain are called into action to store a single memory. In studies with mice, the researchers discovered that to maintain certain short-term memories, the brain’s cortex — the outer layer of tissue thought to be responsible for generating most thoughts and actions — relies on connections with a small region in the center of the brain called the thalamus.

The thalamus is best known as a relay center that passes incoming sensory information to other parts of the brain for processing. But clinical findings suggested that certain parts of the thalamus might also play a critical role in consciousness and cognitive function. The discovery that the thalamus is needed to briefly store information so that animals can act on a past experience demonstrates that the region has a powerful influence on the function of the cortex, says Janelia group leader Karel Svoboda, who led the study. “It really suggests that cortex by itself cannot maintain these memories,” he says. “Instead the thalamus is an important participant.”

Svoboda, Janelia group leader Shaul Druckmann, and their colleagues reported their findings in the May 11, 2017, issue of the journal Nature.

When a memory is formed in the brain, activity in the cells that store the information changes for the duration of the memory. Since individual neurons cannot remain active for more than a few milliseconds on their own, groups of cells work together to store the information. Neurons signaling back and forth can sustain one another’s activity for the seconds that it takes to store a short-term memory.

Svoboda wants to understand exactly how such memories are formed and maintained, including where in the brain they are stored. In prior work, his team determined that in mice, a region of the cortex called the anterior lateral motor cortex (ALM) is critical for short-term memory. Activity in this area is necessary for mice to perform a memory-related task in which they experience a sensory cue that they must remember for several seconds before they are given an opportunity to act on the cue and earn a reward.

Svoboda and his colleagues wanted to understand if ALM stores these memories by itself, or if other parts of the brain work in concert with the ALM to store memories. ALM connects to several other brain regions via long-range connections. The next step was to investigate whether any of the region’s long-range communications were important for memory storage.

Zengcai Guo and Hidehiko Inagaki, postdoctoral researchers in Svoboda’s lab, tested those connections one by one, evaluating whether switching off neurons in various brain regions interfered with memory-associated activity in the ALM and impacted animals’ ability to remember their cues.

The results were clear. “The only player that perturbed the memory was the thalamus,” Svoboda says. “And it was an incredibly dramatic effect. If you turn off these thalamic neurons, activity and short-term memories completely disappear in the cortex. The cortex effectively becomes comatose.”

In further experiments, the team discovered that information flows both ways between the thalamus and the ALM portion of the cortex. “It’s like a game of ping-pong,” Svoboda says. “One excites the other, and the other then excites the first, and so on and so forth. This back and forth maintains these activity patterns that correspond to the memory.”

The finding highlights the functional importance of connections between distant parts of the brain, which Svoboda says are often neglected as neuroscientists focus their attention on activity within particular regions. “It was unexpected that these short-term memories are maintained in a thalamocortical loop,” he says. “This tells us that these memories are widely distributed across the brain.”

Source:Science Daily