Department of Biology, University of Pennsylvania, Philadelphia, PA 19104.
Department of Plant Biology, University of California, Davis, CA 95616.
Proc Natl Acad Sci U S A. 2019 Jul 30;116(31):15596-15601. doi: 10.1073/pnas.1900644116. Epub 2019 Jul 15.
Age-dependent changes in plant defense against herbivores are widespread, but why these changes exist remains a mystery. We explored this question by examining a suite of traits required for the interaction between swollen thorn acacias (genus ) and ants of the genus In this system, plants provide ants with refuge and food in the form of swollen stipular spines, protein-lipid-rich "Beltian" bodies, and sugar-secreting extrafloral nectaries-the "swollen thorn syndrome." We show that this syndrome develops at a predictable time in shoot development and is tightly associated with the temporal decline in the microRNAs miR156 and miR157 and a corresponding increase in their targets-the SPL transcription factors. Growth under reduced light intensity delays both the decline in miR156/157 and the development of the swollen thorn syndrome, supporting the conclusion that these traits are controlled by the miR156-SPL pathway. Production of extrafloral nectaries by sp. that do not house ants is also correlated with a decline in miR156/157, suggesting that this syndrome evolved by co-opting a preexisting age-dependent program. Along with genetic evidence from other model systems, these findings support the hypothesis that the age-dependent development of the swollen thorn syndrome is a consequence of genetic regulation rather than a passive developmental pattern arising from developmental constraints on when these traits can develop.
植物对草食动物防御的年龄依赖性变化很普遍，但这些变化为何存在仍然是个谜。我们通过研究肿胀刺金合欢（属）与 属蚂蚁之间相互作用所需的一系列特征来探讨这个问题。在这个系统中，植物以肿胀的托叶刺、富含蛋白质和脂质的“ Beltian ”体以及分泌糖分的额外花外蜜腺——“肿胀刺综合征”为蚂蚁提供庇护所和食物。我们表明，这种综合征在芽发育的可预测时间内发展，并与 microRNAs miR156 和 miR157 的时间下降以及其靶标——SPL 转录因子的相应增加密切相关。在低光照强度下生长会延迟 miR156/157 的下降和肿胀刺综合征的发展，这支持了这些特征受 miR156-SPL 途径控制的结论。不饲养蚂蚁的 种产生额外的花蜜腺与 miR156/157 的下降也有关，这表明这种综合征是通过利用预先存在的年龄依赖性程序进化而来的。这些发现与来自其他模式系统的遗传证据一起，支持了这样一种假设，即肿胀刺综合征的年龄依赖性发展是遗传调控的结果，而不是由于这些特征在何时发育的发育限制而产生的被动发育模式。
