PREMISE Light is critical in the ability of plants to accumulate chlorophyll. When exposed to far-red (FR) light and then grown in white light in the absence of sucrose, wild-type seedlings fail to green in a response known as the FR block of greening (BOG). This response is controlled by phytochrome A through repression of protochlorophyllide reductase-encoding (POR) genes by FR light coupled with irreversible plastid damage. Sigma (SIG) factors are nuclear-encoded proteins that contribute to plant greening and plastid development through regulating gene transcription in chloroplasts and impacting retrograde signaling from the plastid to nucleus. SIGs are regulated by phytochromes, and the expression of some SIG factors is reduced in phytochrome mutant lines, including phyA. Given the association of phyA with the FR BOG and its regulation of SIG factors, we investigated the potential regulatory role of SIG factors in the FR BOG response. METHODS We examined FR BOG responses in sig mutants, phytochrome-deficient lines, and mutant lines for several phy-associated factors. We quantified chlorophyll levels and examined expression of key BOG-associated genes. RESULTS Among six sig mutants, only the sig6 mutant significantly accumulated chlorophyll after FR BOG treatment, similar to the phyA mutant. SIG6 appears to control protochlorophyllide accumulation by contributing to the regulation of tetrapyrrole biosynthesis associated with glutamyl-tRNA reductase (HEMA1) function, select phytochrome-interacting factor genes (PIF4 and PIF6), and PENTA1, which regulates PORA mRNA translation after FR exposure. CONCLUSIONS Regulation of SIG6 plays a significant role in plant responses to FR exposure during the BOG response.

中文翻译：

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核编码的 sigma 因子 6 (SIG 6) 参与了拟南芥绿化反应的阻断

PREMISE Light 对植物积累叶绿素的能力至关重要。当暴露在远红 (FR) 光下，然后在没有蔗糖的情况下在白光下生长时，野生型幼苗在称为 FR 绿化 (BOG) 的反应中无法变绿。这种反应由光敏色素 A 通过 FR 光抑制原叶绿素还原酶编码 (POR) 基因和不可逆的质体损伤来控制。Sigma (SIG) 因子是核编码蛋白，通过调节叶绿体中的基因转录和影响从质体到细胞核的逆行信号传导，有助于植物绿化和质体发育。SIGs 受光敏色素的调节，一些 SIG 因子的表达在光敏色素突变株系中减少，包括 phyA。鉴于 phyA 与 FR BOG 的关联及其对 SIG 因子的调节，我们研究了 SIG 因子在 FR BOG 反应中的潜在调节作用。方法 我们检查了 sig 突变体、光敏色素缺陷系和突变系中几种 phy 相关因子的 FR BOG 反应。我们量化了叶绿素水平并检查了关键 BOG 相关基因的表达。结果在6个sig突变体中，只有sig6突变体在FR BOG处理后叶绿素显着积累，与phyA突变体相似。SIG6 似乎通过调节与谷氨酰-tRNA 还原酶 (HEMA1) 功能相关的四吡咯生物合成、选择光敏色素相互作用因子基因（PIF4 和 PIF6）和 PENTA1 来控制原叶绿素积累，后者在 FR 暴露后调节 PORA mRNA 翻译。