水稻白叶枯病菌无毒蛋白AX21的研究论文作者主动退回发表论文

——两篇关于植物免疫功能的论文被退回。

在几年前，由于两个细菌样品出现了标示错误，而导致两篇论文被退回，其中一篇就是发表于《Science》杂志上的高引用论文：A Type I–Secreted, Sulfated Peptide Triggers XA21 -Mediated Innate Immunity。

这篇论文是2009年，由加州大学戴维斯分校植物遗传学家Pamela Ronald领导完成，研究报道称他们发现了水稻免疫系统识别的一个细菌分子，这项研究是这一实验室长期研究的成果，有助于解析这种重要的农作物如何抵抗感染。目前论文已经被引用131次。

但是之后新实验室成员无法重复出先前的结果，经过分析，研究小组发现之前的实验采用了贴错标签的细菌菌株，Ronald在该领域的会议上宣布的这一问题，目前论文已经被撤回。

“包括进行最初工作的研究人员在内，都不存在任何问题，论文错了，我们就毫不犹豫的撤回论文，”Ronald说，“我们不想误导任何人。”

在1995年，Ronald的研究小组发现，一种称为XA21蛋白的受体能帮助水稻抵抗白叶枯病菌（Xanthomonas oryzae）的致病细菌。后来研究人员也在人体，小鼠和其它动物中发现了相似的蛋白质。

Xa21基因是第一个从野生稻中被克隆出来的重要功能基因，Ronald等人将Xa21定位于第11染色体上，与RAPD818、RAPD248和RG103标记的遗传图距都不超过1.2cM。随后该基因由宋文元等克隆，并迅速广泛应用于国内外水稻抗白叶枯病转基因育种。

将近十五年后，Ronald研究组又指出，XA21能识别一种称为AX21的细菌蛋白。他们发现一种AX21缺陷型突变株白叶枯病菌可以成功地感染水稻叶片。如果没有这种细菌的识别标志-即AX21蛋白，那么XA21就无法完成免疫反应。“这一发现对于我们来说意义重大，”Ronald说。

但是此后这一实验室的新成员却无法重复先前的实验。新的实验多次表明，水稻植株可以抵御AX21缺陷型的白叶枯病菌（即AX21 缺陷型突变株白叶枯病菌不能成功地感染水稻叶片）。

最终研究人员发现原来是之前的12个突变株中有两个被贴错了标签。这意味着XA21识别的分子仍是一个谜，而且更糟的是，这一研究小组发现的另一个重要结果——合成的AX21可能会引发水稻的免疫反应，也是一个不可靠的结果，因为无法被重复。

虽然Ronald认为论文其他方面仍然是有效的，但她不希望误导其他实验室，因此去年她撤回了这篇论文，同时也撤回了另外一篇2011年发表在《PLoS ONE》上的文章。

Two samples of bacteria that were mislabeled several years ago have led to the retraction of two papers, includinga highly-cited one published inScience.

In 2009, a team of scientists from theUniversityofCalifornia,Davis, led by plant geneticist Pamela Ronald, identified a bacterial molecule that is recognized by the immune system of rice plants. It was the culmination of the lab’s longstanding quest to understand how this vital crop thwarts infections, and the paper has since been cited 131 times.

But when new lab members could not repeat the earlier results, the team discovered that one of the previous experiments had been done with mislabeled bacterial strains, while another had used an unreliable test. Ronald announced the problems to others in the field at conferences, and has now retracted the paper.

“There was never any question, even from the people who did the original work, that we do anything different than retract the paper if it was wrong,” said Ronald. “We didn’t want to mislead anyone else.”

The most common causes of scientific retractions are misconduct or fraud, discovered through the actions of whistleblowers or watchful peers. It is rarer to see labs discover and own up to their own honest errors. “Too often, scientists, their institutions, and journals find ways to sweep painful reality under the rug, or make half-hearted attempts to correct the literature,” says Ivan Oransky, a journalist who monitors scientific retractions through his blogRetraction Watch. “For a researcher to go out of her way to publicize her mistakes is unfortunately very unusual. Some scientists worry that retractions lead to a mistrust of science, but when handled appropriately the way Ronald’s have been, they only boost public confidence in research.”

In 1995, Ronald’s team showed that a receptor protein called XA21 allows rice plants to resist a devastating disease-causing bacterium calledXanthomonas oryzae. Many similar proteins were later discovered in humans, mice and other animals. Known as pattern recognition receptors (PRRs), their hallmark is the ability to recognise molecules found in a wide range of bacteria and trigger an immune reaction.

Nearly 15 years later, the team revealed that XA21 recognizes a bacterial protein called Ax21—the key to its lock. In a critical experiment, they showed that a mutant strain ofX.oryzae, which lacked the gene for Ax21, can successfully infect rice leaves. Without this bacterial identity badge, XA21 could not mount an immune response. “The discovery made a lot of sense to us, and it seemed to fit everything that we and others had shown before,” said Ronald, whose results were published in 2009 inScience. “It was a very exciting time.”

The first hint of trouble came in June 2012. As is traditional for Ronald’s lab, a couple of new members tried to repeat the earlier experiments. But time and again, they failed. The new experiments repeatedly showed that rice plants could still resistX. oryzaestrains that lacked Ax21.

“It’s tricky to work with rice, and they thought they were getting the experiments wrong,” said Ronald. But they eventually found that the 2 of the 12 original mutant strains had been mislabeled. Rather than Ax21, they were missing a different protein called RaxSt. “As far as we can figure out, it was just a mix-up,” said Ronald. “One team member gave it to another, and the one who did the experiment didn’t double-check. We should’ve caught it sooner.”

The revelation means that the molecule that XA21 recognizes is still a mystery. Ronald thinks that the mislabeled strains slipped past rice defenses because RaxSt modifies the unknown molecule, so that XA21 can recognize it. “We still don’t know what it is, and we’re trying to find it,” said Ronald. “It’s back to the drawing board.”

To make matters worse, the team found that another key result—that a synthetic version of Ax21 could trigger an immune response in rice—depended on an unreliable test, and could also not be consistently repeated.

Although Ronald feels that other aspects of the paper are still valid, she did not want the mistakes to waylay other labs while her team repeated the other experiments. She announced the problems at aplant immunity conferencelast April, and contactedScienceto retract the paper. “I wanted to be sure that we got the word out early,” she said. The mislabeled strain was also used in experiments in a second paper, which waspublished in 2011 inPLOS ONEand wasalso retracted last month.

“Sorting out the situation was personally and professionally painful for all involved,” Ronald wrote in anew blog post. “Former lab members who had begun new positions as professors inKoreaandThailandwere devastated to learn that [we] could not repeat their work. Junior scientists in the laboratory worried their careers would be tarnished. . . . It took persistence, courage and confidence to stick together as a team throughout this challenging year.”

The mistakes might never have been found at all if her lab did not commonly repeat old experiments, but Ronald is reticent to prescribe the same approach for other groups. “It’s just not realistic for most labs,” she toldThe Scientist. “Scientists move on, projects move on, there are funding issues. The bigger lesson is probably what we already know: you can’t rely on a single published report, or even more than that.”

Other scientists in the field have taken the retractions in good faith. “I feel absolutely confident that there was no intentional cheating,” said Markus Albert, a plant biologist from theUniversityofTubingen. Purifying and identifying the molecules that are recognized by PRRs “was, and still is, a difficult topic,” he said. “Otherwise, more of them would have been identified [by now].”

To complicate matters, at leastthreeChineselabshave successfully replicated Ronald’s Ax21 experiments. “I’ve talked to all the other laboratories, and they’re all confident in their results,” Ronald said. Wenxian Sun fromChinaAgriculturalUniversity, who led one of the studiespublished online inPhytopathology, said that he has delayed formal publication until he can repeat the key results. The other teams did not respond to requests for comments.

“The fact that several labs have reported what might now be viewed as questionable data makes one pause,” saidSophien Kamoun, a plant biologist at the Sainsbury Laboratory. Along with the Chinese studies, he points to three other papers that are either “compromised or questionable” because they also involve Ax21:one from Ronald’s group, which found that XA21 gets cut and relocated after exposure to Ax21;one that lists Ronald as a collaborator, which found that Ax21 interacts with another immune receptor called FLS2;and a third from an independent lab, which found that some bacteria use Ax21 to communicate with each other—a similar result to Ronald’s now-retractedPLOS ONEpaper.

“I truly hope to see the authors of papers that are based on Ax21 come forward to clarify their work,” Kamoun said.