The constitutively active missense allele of Arabidopsis phytochrome B, AtPHYB^Y276H or AtYHB, encodes a polypeptide that adopts a light‐insensitive, physiologically active conformation capable of sustaining photomorphogenesis in darkness. Here, we show that the orthologous OsYHB allele of rice phytochrome B (OsPHYB^Y283H) also encodes a dominant “constitutively active” photoreceptor through comparative phenotypic analyses of AtYHB and OsYHB transgenic lines of four eudicot species, Arabidopsis thaliana, Nicotiana tabacum (tobacco), Nicotiana sylvestris and Solanum lycopersicum cv. MicroTom (tomato), and of two monocot species, Oryza sativa ssp. japonica and Brachypodium distachyon. Reciprocal transformation experiments show that the gain‐of‐function constitutive photomorphogenic (cop) phenotypes by YHB expression are stronger in host plants within the same class than across classes. Our studies also reveal additional YHB‐dependent traits in adult plants, which include extreme shade tolerance, both early and late flowering behaviors, delayed leaf senescence, reduced tillering, and even viviparous seed germination. However, the strength of these gain‐of‐function phenotypes depends on the specific combination of YHB allele and species/cultivar transformed. Flowering and tillering of OsYHB‐ and OsPHYB‐expressing lines of rice Nipponbare and Kitaake cultivars were compared, also revealing differences in YHB/PHYB allele versus genotype interaction on the phenotypic behavior of the two rice cultivars. In view of recent evidence that the regulatory activity of AtYHB is not only light insensitive but also temperature insensitive, selective YHB expression is expected to yield improved agronomic performance of both dicot and monocot crop plant species not possible with wild‐type PHYB alleles.

中文翻译：

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利用光敏色素 B 组成型活性等位基因调节单子叶植物和双子叶植物发育。


拟南芥光敏色素 B 的组成型活性错义等位基因AtPHYB ^Y276H或AtYHB编码一种多肽，该多肽采用光不敏感的生理活性构象，能够在黑暗中维持光形态发生。在这里，我们通过对拟南芥、烟草、烟草等四种真双子叶植物的AtYHB和OsYHB转基因系的比较表型分析，发现水稻光敏色素 B 的直系同源OsYHB等位基因 ( OsPHYB ^Y283H ) 也编码显性的“组成型活性”光感受器。烟草 (Nicotiana sylvestris)和番茄 (Solanum lycopersicum) cv. MicroTom（番茄），以及两个单子叶植物物种Oryza sativa ssp。粳稻和二穗短柄草。相互转化实验表明，通过YHB表达获得的功能获得性光形态发生 ( cop ) 表型在同一类寄主植物中比跨类更强。我们的研究还揭示了成年植物的其他YHB依赖性性状，其中包括极端的耐荫性、早花和晚花行为、延迟叶片衰老、减少分蘖，甚至胎生种子萌发。然而，这些功能获得表型的强度取决于YHB等位基因和转化的物种/品种的特定组合。 对水稻 Nipponbare 和 Kitaake 品种的OsYHB和OsPHYB表达系的开花和分蘖进行了比较，还揭示了YHB/PHYB等位基因与基因型相互作用对两个水稻品种表型行为的差异。鉴于最近的证据表明At YHB 的调节活性不仅对光不敏感，而且对温度不敏感，选择性YHB表达预计将改善双子叶和单子叶作物植物的农艺性能，这是野生型PHYB等位基因不可能实现的。