Water-Soluble Lignins from Different Bioenergy Crops Stimulate the Early Development of Maize (Zea mays, L.).

The molecular composition of water-soluble lignins isolated from four non-food bioenergy crops (cardoon CAR, eucalyptus EUC, and two black poplars RIP and LIM) was characterized in detail, and their potential bioactivity towards maize germination and early growth evaluated. Lignins were found to not affect seed germination rates, but stimulated the maize seedling development, though to a different extent. RIP promoted root elongation, while CAR only stimulated the length of lateral seminal roots and coleoptile, and LIM improved only the coleoptile development. The most significant bioactivity of CAR was related to its large content of aliphatic OH groups, C-O carbons and lowest hydrophobicity, as assessed by (31)P-NMR and (13)C-CPMAS-NMR spectroscopies. Less bioactive RIP and LIM lignins were similar in composition, but their stimulation of maize seedling was different. This was accounted to their diverse content of aliphatic OH groups and S- and G-type molecules. The poorest bioactivity of the EUC lignin was attributed to its smallest content of aliphatic OH groups and largest hydrophobicity. Both these features may be conducive of a EUC conformational structure tight enough to prevent its alteration by organic acids exuded from vegetal tissues. Conversely the more labile conformational arrangements of the other more hydrophilic lignin extracts promoted their bioactivity by releasing biologically active molecules upon the action of exuded organic acids. Our findings indicate that water-soluble lignins from non-food crops may be effectively used as plant biostimulants, thus contributing to increase the economic and ecological liability of bio-based industries.

Transcriptome Analysis Revealed the Key Genes and Pathways Involved in Seed Germination of Maize Tolerant to Deep-Sowing.

To improve our understanding of the mechanism of maize seed germination under deep sowing, transcriptome sequencing and physiological metabolism analyses were performed using B73 embryos separated from ungerminated seeds (UG) or seeds germinated for 2 d at a depth of 2 cm (normal sowing, NS) or 20 cm (deep sowing, DS). Gene ontology (GO) analysis indicated that "response to oxidative stress" and "monolayer-surrounded lipid storage body" were the most significant GO terms in up- and down-regulated differentially expressed genes (DEGs) of DS. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis suggested that "phenylpropanoid biosynthesis" and "starch and sucrose metabolism" were critical processes in maize seed germination under deep-sowing conditions. Consistent with DEGs, the activities of superoxide dismutase, catalase, peroxidases and α-amylase, as well as the contents of gibberellin 4, indole acetic acid, zeatin and abscisic acid were significantly increased, while the jasmonic-acid level was dramatically reduced under deep-sowing stress. The expressions of six candidate genes were more significantly upregulated in B73 (deep-sowing-tolerant) than in Mo17 (deep-sowing-sensitive) at 20 cm sowing depth. These findings enrich our knowledge of the key biochemical pathways and genes regulating maize seed germination under deep-sowing conditions, which may help in the breeding of varieties tolerant to deep sowing.

Transcriptomic and Metabolic Profiling Reveals a Lignin Metabolism Network Involved in Mesocotyl Elongation during Maize Seed Germination.

Lignin is an important factor affecting agricultural traits. The mechanism of lignin metabolism in maize (Zea mays) mesocotyl elongation was investigated during seed germination. Maize seeds were treated with 24-epibrassinolide (EBR) and brassinazole stimulation under 3 and 20 cm deep-seeding stress. Mesocotyl transcriptome sequencing together with targeted metabolomics analysis and physiological measurements were employed in two contrasting genotypes. Our results revealed differentially expressed genes (DEGs) were significantly enriched in phenylpropanoid biosynthesis, plant hormone signal transduction, flavonoid biosynthesis, and alpha-linolenic acid metabolism. There were 153 DEGs for lignin biosynthesis pathway, 70 DEGs for peroxisome pathway, and 325 differentially expressed transcription factors (TFs) of MYB, NAC, WRKY, and LIM were identified in all comparisons, and highly interconnected network maps were generated among multiple TFs (MYB and WRKY) and DEGs for lignin biosynthesis and peroxisome biogenesis. This caused p-coumaraldehyde, p-coumaryl alcohol, and sinapaldehyde down-accumulation, however, caffeyl aldehyde and caffeyl alcohol up-accumulation. The sum/ratios of H-, S-, and G-lignin monomers was also altered, which decreased total lignin formation and accumulation, resulting in cell wall rigidity decreasing. As a result, a significant elongation of maize mesocotyl was detected under deep-seeding stress and EBR signaling. These findings provide information on the molecular mechanisms controlling maize seedling emergence under deep-seeding stress and will aid in the breeding of deep-seeding maize cultivars.