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Title: Nuclear‐encoded sigma factor 6 ( SIG 6) is involved in the block of greening response in Arabidopsis thaliana

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 theFRblock of greening (BOG). This response is controlled by phytochrome A through repression of protochlorophyllide reductase‐encoding (POR) genes byFRlight 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 someSIGfactors is reduced in phytochrome mutant lines, including phyA. Given the association of phyA with theFR BOGand its regulation ofSIGfactors, we investigated the potential regulatory role ofSIGfactors in theFR BOGresponse.


We examinedFR BOGresponses insigmutants, phytochrome‐deficient lines, and mutant lines for several phy‐associated factors. We quantified chlorophyll levels and examined expression of keyBOG‐associated genes.


Among sixsigmutants, only thesig6 mutant significantly accumulated chlorophyll afterFR BOGtreatment, similar to thephyAmutant.SIG6 appears to control protochlorophyllide accumulation by contributing to the regulation of tetrapyrrole biosynthesis associated with glutamyl‐tRNAreductase (HEMA1) function, select phytochrome‐interacting factor genes (PIF4andPIF6), andPENTA1, which regulatesPORAmRNAtranslation afterFRexposure.


Regulation ofSIG6plays a significant role in plant responses toFRexposure during theBOGresponse.

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Author(s) / Creator(s):
 ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
American Journal of Botany
Page Range / eLocation ID:
p. 329-338
Medium: X
Sponsoring Org:
National Science Foundation
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