Greenbeard genetic elements encode rare perceptible signals, signal recognition ability, and altruism towards others that display the same signal. Putative greenbeards have been described in various organisms but direct evidence for all the properties in one system is scarce. The tgrB1-tgrC1 allorecognition system of Dictyostelium discoideum encodes two polymorphic membrane proteins which protect cells from chimerism-associated perils. During development, TgrC1 functions as a ligand-signal and TgrB1 as its receptor, but evidence for altruism has been indirect. Here, we show that mixing wild-type and activated tgrB1 cells increases wild-type spore production and relegates the mutants to the altruistic stalk, whereas mixing wild-type and tgrB1-null cells increases mutant spore production and wild-type stalk production. The tgrB1-null cells cheat only on partners that carry the same tgrC1-allotype. Therefore, TgrB1 activation confers altruism whereas TgrB1 inactivation causes allotype-specific cheating, supporting the greenbeard concept and providing insight into the relationship between allorecognition, altruism, and exploitation.

绿胡子的遗传元素编码罕见的可感知信号、信号识别能力以及对显示相同信号的其他人的利他主义。假定的绿胡子已在多种生物体中得到描述，但一个系统中所有特性的直接证据却很少。盘基网柄菌的tgrB1-tgrC1同种识别系统编码两种多态性膜蛋白，可保护细胞免受嵌合相关的危险。在发育过程中，TgrC1 作为配体信号，TgrB1 作为其受体，但利他主义的证据是间接的。在这里，我们表明，混合野生型和活化的tgrB1细胞会增加野生型孢子的产生，并将突变体降级为利他茎，而混合野生型和tgrB1无效细胞会增加突变体孢子的产生和野生型茎的产生。 tgrB1无效细胞仅欺骗携带相同tgrC1同种异型的伴侣。因此，TgrB1 激活赋予利他主义，而 TgrB1 失活则导致同种异型特异性作弊，支持绿胡子概念并提供对同种异体识别、利他主义和剥削之间关系的见解。