Greening immediately after etiolated- seedling's emergence from the soil is critical for plants to initiate their autotrophic life cycle through photosynthesis. The greening process relies on a complex transcriptional network that fine- tunes the biosynthesis of chlorophyll and prevents premature development of chloroplasts. In this study, we identified the Arabidopsis HOOKLESS1 (HLS1) as a key regulator of light- induced cotyledon greening. Our results demonstrated that HLS1 is essential for the proper expression of greening- related genes controlling chlorophyll biosynthesis and chloroplast development. Loss of HLS1 severely disrupts the Pchlide- to- Chlide transition and impairs reactive oxygen species (ROS) scavenging in etiolated seedlings upon light exposure, leading to catastrophic ROS burst and even photobleaching. Biochemical assays revealed that HLS1 is a histone acetyltransferase mediating the deposition of H3K9ac and H3K27ac marks at multiple greening- related genes, thereby promoting their transcriptional activation. Genetic analysis further confirmed that HLS1's promotive effect on the greening process is fully dependent on its histone acetyltransferase activity. Moreover, the loss of HLS1 also interrupts the promotive effect of ethylene signaling on the greening process by reducing the binding of ETHYLENE- INSENSITIVE 3 to the promoter region of POR genes, thus inhibiting the activation effect of ethylene signaling on the expression of PORs. Collectively, our study reveals that HLS1 acetylates histones to activate greening- related genes, optimizing chlorophyll biosynthesis and chloroplast development during dark- to- light transition in seedlings.

Cellulose micro-nanofibrils (CMNF) with different fibrillation levels were partially acetylated while preserving their morphological and native crystalline structure. The morphological changes due to fibrillation and chemical modification were observed using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and optical profilometry. The change in tensile and burst strength, barrier, and biodegradability profile were investigated which revealed that the mechanical properties of the unmodified CMNF films increased with increase in extent of fibrillation. However, the mechanical strength of the acetylated film decreased with the increase in degree of acetylation. The stretching or folding property of the film increased with the increase in both the fibrillation and acetylation. The contact angle value increased due to a higher degree of fibrillation and acetylation because they increased the hydrophobicity and consequently enhanced the air and water vapor resistance of the unmodified and modified CNF films. Furthermore, all films exhibited the highest resistance against oil and grease, and the biodegradability test substantiated that CNF films were compostable in soil. In total, this work expresses new pathways to enhance the barrier properties of biodegradable CNF films by regulating the degree of fibrillation and acetylation, thus can emerge as sustainable alternatives for packaging and agriculture applications.