The type and content of starch are believed to be the most critical factors in determining the storage and processing quality of lotus rhizome species, and the intention of this study is to survey the structure and properties of starches isolated from rhizomes of two lotus cultivars using X‐ray powder diffraction, solid‐state nuclear magnetic resonance spectroscopy, attenuated total reflectance‐Fourier transform infrared spectroscopy, scanning electron microscope, differential scanning calorimetry, and rapid viscosity analyzer (RVA). Starch in rhizome of cultivar Meirenhong exhibited C‐type X‐ray diffraction pattern, while starch in rhizome of cultivar Wawalian showed A‐type pattern. ¹³C cross‐polarization magic‐angle spinning nuclear magnetic resonance (¹³C CP‐MAS NMR) also confirmed the polymorphs. The relative crystallinity of two starches was quantitatively estimated from two methods and compared. Attenuated total reflectance‐Fourier transform infrared (ATR‐FTIR) results indicated that the external regions of the starch granules had a great level of ordered structure. Starch granules in Meirenhong showed oval‐shaped granules, while starch granules in Wawalian were elongated and oval in shape with relatively large size. Gelatinization temperatures of starch in Meirenhong and Wawalian were 330.5 and 342.4 K, respectively, and the gelatinization temperature range of Meirenhong was significantly wider than that of Wawalian. Starch in rhizome of cultivar Meirenhong showed lower pasting temperature, lower hot and cool viscosities, lower setback, and higher peak viscosity and breakdown than those of Wawalian in RVA pasting profiles at 6% starch concentration.

Lotus root is a popular wetland vegetable which produces edible rhizome. At the molecular level, the regulation of rhizome formation is very complex, which has not been sufficiently addressed in research. In this study, to identify differentially expressed genes (DEGs) in lotus root, four libraries (L1 library: stolon stage, L2 library: initial swelling stage, L3 library: middle swelling stage, L4: later swelling stage) were constructed from the rhizome development stages. High-throughput tag-sequencing technique was used which is based on Solexa Genome Analyzer Platform. Approximately 5.0 million tags were sequenced, and 4542104, 4474755, 4777919, and 4750348 clean tags including 151282, 137476, 215872, and 166005 distinct tags were obtained after removal of low quality tags from each library respectively. More than 43% distinct tags were unambiguous tags mapping to the reference genes, and 40% were unambiguous tag-mapped genes. From L1, L2, L3, and L4, total 20471, 18785, 23448, and 21778 genes were annotated, after mapping their functions in existing databases. Profiling of gene expression in L1/L2, L2/L3, and L3/L4 libraries were different among most of the selected 20 DEGs. Most of the DEGs in L1/L2 libraries were relevant to fiber development and stress response, while in L2/L3 and L3/L4 libraries, major of the DEGs were involved in metabolism of energy and storage. All up-regulated transcriptional factors in four libraries and 14 important rhizome formation-related genes in four libraries were also identified. In addition, the expression of 9 genes from identified DEGs was performed by qRT-PCR method. In a summary, this study provides a comprehensive understanding of gene expression during the rhizome formation in lotus root.

Euryale ferox Salisb., an annual aquatic plant, is the only species in the genus Euryale in the Nymphaeaceae. Seeds of E. ferox are a nutritious food and also used in traditional Chinese medicine (Qian Shi in Mandarin). The molecular events that occurred during seed development in E. ferox have not yet been characterized. In this study, we performed transcriptomic analysis of four developmental stages (T1, T2, T3, and T4) in E. ferox seeds with three biological replicates per developmental stage to understand the physiological and biochemical processes during E. ferox seeds development. 313,844,425 clean reads were assembled into 160,107 transcripts and 85,006 unigenes with N50 lengths of 2052 bp and 1399 bp, respectively. The unigenes were annotated using five public databases (NR, COG, Swiss-Prot, KEGG, and GO). In the KEGG database, all of the unigenes were assigned to 127 pathways, of which phenylpropanoid biosynthesis was associated with the synthesis of secondary metabolites during E. ferox seed growth and development. Phenylalanine ammonia-lyase (PAL) as the first key enzyme catalyzed the conversion of phenylalanine to trans-cinnamic acid, then was related to the synthesis of flavonoids, lignins and alkaloid. The expression of PAL1 reached its peak at T3 stage, followed by a slight decrease at T4 stage. Cytochrome P450 (P450), encoded by CYP84A1 (which also called ferulate-5-hydroxylase (F5H) in Arabidopsis), was mainly involved in the biosynthesis of lignins. Our study provides a transcriptomic analysis to better understand the morphological changes and the accumulation of medicinal components during E. ferox seed development. The increasing expression of PAL and P450 encoded genes in phenylpropanoid biosynthesis may promote the maturation of E. ferox seed including size, color, hardness and accumulation of medicinal components.

SUMMARY: Occupation of living space is one of the main driving forces of adaptive evolution, especially for aquatic plants whose leaves float on the water surface and thus have limited living space. Euryale ferox, from the angiosperm basal family Nymphaeaceae, develops large, rapidly expanding leaves to compete for space on the water surface. Microscopic observation found that the cell proliferation of leaves is almost completed underwater, while the cell expansion occurs rapidly after they grow above water. To explore the mechanism underlying the specific development of leaves, we performed sequences assembly and analyzed the genome and transcriptome dynamics of E. ferox. Through reconstruction of the three sub‐genomes generated from the paleo‐hexaploidization event in E. ferox, we revealed that one sub‐genome was phylogenetically closer to Victoria cruziana, which also exhibits gigantic floating leaves. Further analysis revealed that while all three sub‐genomes promoted the evolution of the specific leaf development in E. ferox, the genes from the sub‐genome closer to V. cruziana contributed more to this adaptive evolution. Moreover, we found that genes involved in cell proliferation and expansion, photosynthesis, and energy transportation were over‐retained and showed strong expression association with the leaf development stages, such as the expression divergence of SWEET orthologs as energy uploaders and unloaders in the sink and source leaf organs of E. ferox. These findings provide novel insights into the genome evolution through polyploidization, as well as the adaptive evolution regarding the leaf development accomplished through biased gene retention and expression sub‐functionalization of multi‐copy genes in E. ferox.