Seed deterioration during rice seed storage can lead to seed vigor loss, which adversely affects agricultural production, the long-term preservation of germplasm resources, and the conservation of species diversity. However, the mechanisms underlying seed vigor maintenance remain largely unknown. In this study, 16 hybrid rice combinations were created using four sterile lines and four restorer lines that have been widely planted in southern China. Following artificial aging and natural aging treatments, germination percentage and metabolomics analysis by gas chromatography–mass spectrometry was used to identify the metabolite markers that could accurately reflect the degree of aging of the hybrid rice seeds. Significant differences in the degree of seed deterioration were observed among the 16 hybrid rice combinations tested, with each hybrid combination having a different germination percentage after storage. The hybrid rice combination with the storage-resistant restorer line Guanghui122 exhibited the highest germination percentage under both natural and artificial storage. A total of 89 metabolic peaks and 56 metabolites were identified, most of which were related to primary metabolism. Interestingly, the content of galactose, gluconic acid, fructose and glycerol in the seeds increased significantly during the aging process. Absolute quantification indicated that galactose and gluconic acid were highly significantly negatively correlated with the germination percentage of the seeds under the different aging treatments. The galactose content was significantly positively correlated with gluconic acid content. Additionally, glycerol showed a significant negative correlation with the germination percentage in most hybrid combinations. Based on the metabolomics analysis, metabolite markers that could accurately reflect the aging degree of hybrid rice seeds were identified. Galactose and gluconic acid were highly significantly negatively correlated with the germination percentage of the seeds, which suggested that these metabolites could constitute potential metabolic markers of seed vigor and aging. These findings are of great significance for the rapid and accurate evaluation of seed aging degree, the determination of seed quality, and the development of molecular breeding approaches for high-vigor rice seeds.

PICKLE (PKL) is a chromodomain helicase DNA-binding domain 3 (CHD3) chromatin remodeler that plays essential roles in controlling the gene expression patterns that determine developmental identity in plants, but the molecular mechanisms through which PKL is recruited to its target genes remain elusive. Here, we define a cis-motif and trans-acting factors mechanism that governs the genomic occupancy profile of PKL in Arabidopsis thaliana. We show that two homologous trans-factors VIVIPAROUS1/ABI3-LIKE1 (VAL1) and VAL2 physically interact with PKL in vivo, localize extensively to PKL-occupied regions in the genome, and promote efficient PKL recruitment at thousands of target genes, including those involved in seed maturation. Transcriptome analysis and genetic interaction studies reveal a close cooperation of VAL1/VAL2 and PKL in regulating gene expression and developmental fate. We demonstrate that this recruitment operates at two master regulatory genes, ABSCISIC ACID INSENSITIVE3 and AGAMOUS-LIKE 15, to repress the seed maturation program and ensure the seed-to-seedling transition. Together, our work unveils a general rule through which the CHD3 chromatin remodeler PKL binds to its target chromatin in plants.

Chromatin remodelers have been thought to be crucial in creating an accessible chromatin environment before transcription activation. However, it is still unclear how chromatin remodelers recognize and bind to the active regions. In this study, we found that chromatin remodelers SPLAYED (SYD) and BRAHMA (BRM) interact and co-occupy with Suppressor of Ty6-like (SPT6L), a core subunit of the transcription machinery, at thousands of the transcription start sites (TSS). The association of SYD and BRM to chromatin is dramatically reduced in spt6l and can be restored mainly by SPT6LΔtSH2, which binds to TSS in a RNA polymerase II (Pol II)-independent manner. Furthermore, SPT6L and SYD/BRM are involved in regulating the nucleosome and Pol II occupancy around TSS. The presence of SPT6L is sufficient to restore the association of the chromatin remodeler SYD to chromatin and maintain normal nucleosome occupancy. Our findings suggest that the two chromatin remodelers can form protein complexes with the core subunit of the transcription machinery and regulate nucleosome occupancy in the early transcription stage.

A recently discovered tea [Camellia sinensis (L.) O. Kuntze] cultivar can generate tender shoots in winter. We performed comparative proteomics to analyze the differentially accumulated proteins between winter and spring tender shoots of this clonal cultivar to reveal the physiological basis of its evergrowing character during winter. We extracted proteins from the winter and spring tender shoots (newly formed two leaves and a bud) of the evergrowing tea cultivar “Dongcha11” respectively. Thirty-three differentially accumulated high-confidence proteins were identified by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF / TOF MS). Among these, 24 proteins had increased abundance while nine showed were decreased abundance in winter tender shoots as compared with the spring tender shoots. We categorized the differentially accumulated proteins into eight critical biological processes based on protein function annotation including photosynthesis, cell structure, protein synthesis & destination, transporters, metabolism of sugars and polysaccharides, secondary metabolism, disease/defense and proteins with unknown functions. Proteins with increased abundance in winter tender shoots were mainly related to the processes of photosynthesis, cytoskeleton and protein synthesis, whereas those with decreased abundance were correlated to metabolism and the secondary metabolism of polyphenolic flavonoids. Biochemical analysis showed that the total contents of soluble sugar and amino acid were higher in winter tender shoots while tea polyphenols were lower as compared with spring tender shoots. Our study suggested that the simultaneous increase in the abundance of photosynthesis-related proteins rubisco, plastocyanin, and ATP synthase delta chain, metabolism-related proteins eIF4 and protease subunits, and the cytoskeleton-structure associated proteins phosphatidylinositol transfer protein and profilin may be because of the adaptation of the evergrowing tea cultivar “Dongcha11” to low temperature and light conditions. Histone H4, Histone H2A.1, putative In2.1 protein and protein lin-28 homologs may also regulate the development of winter shoots and their response to adverse conditions.