Morphological and Anatomical Analysis of the Internodes of a New Dwarf Variant of Moso Bamboo, Phyllostachys edulis f. exaurita.

The lack of mutants due to the long periods between flowering of bamboo plants is one of the limiting factors inhibiting research progress in the culm development of bamboo plants. In this study, a stable new dwarf variant of Phyllostachys edulis (Moso bamboo), Phyllostachys edulis f. exaurita T. G. Chen, was discovered and was characterized morphologically, anatomically, and physiologically. The height, diameter at breast height, number of internodes, length and wall thickness of internodes, length, width and number of parenchyma cells of internodes, and morphology of the wide-type (WT) and dwarf variant vascular bundles were compared. The height of the variant was only 49% that of the WT Moso bamboo. It was concluded that the decrease in internode number and length was the cause of dwarfism in P. edulis f. exaurita. The decreased internode length was the result of a decrease in cell number and cell length in the internode. In addition, the laws of change of internode length, internode thickness, cell length, and cell number differed between the WT Moso bamboo and the variant. Furthermore, lower IAA and zeatin concentrations were detected in the buds of the variant. These results suggest that P. edulis f. exaurita is a variant with inhibited primary thickening growth, which is valuable for interpretating the molecular mechanisms underlying the primary thickening growth of bamboo that are still largely unknown.

Histological, metabolomic and transcriptomic analyses reveal mechanisms of cold acclimation of the Moso bamboo (Phyllostachys edulis) leaf.

The Moso bamboo (Phyllostachys edulis) leaf copes well with cold winters in southeastern China. However, until now, there has been almost no research on its adaptation mechanisms to cold weather. Herein, we found that the Moso bamboo leaf has evolved several anatomical structures that may play a role in enhancing its cold tolerance. These structures include fewer fusiform cells, smaller bulliform cells, lower stomata density and many more trichomes, as well as lower relative water content than in the leaf of a cold-sensitive bamboo species, Bambusa ventricosa. Untargeted metabolomic analysis revealed that the winter leaf of Moso bamboo had 10- to 1000-fold higher stress-resistant metabolites such as glutathione, trehalose and ascorbic acid than the leaf of B. ventricosa on both warm and cold days. In contrast to the leaves that grew on a warm day, some metabolites such as glutathione and trehalose increased dramatically in the leaves of Moso bamboo that grew on a cold day. However, they unexpectedly decreased in the leaf of B. ventricosa growing at cold temperatures. Transcriptome analysis revealed a cold stress response network that includes trehalose, glutathione, flavonoid metabolism, DNA repair, reactive oxygen species degradation, stress-associated genes and abiotic stress-related plant hormones such as jasmonic acid, abscisic acid and ethylene. The potential mediator transcription factors, such as EREBP, HSF, MYB, NAC and WRYK, were also significantly upregulated in Moso bamboo leaves growing at cold temperatures. Interestingly, many newly identified genes were involved in the transcriptome of the winter leaf of the Moso bamboo. Most of these new genes have not even been annotated yet. The above results indicate that the Moso bamboo leaf has evolved special histological structures, metabolic pathways and a cold stress-tolerant transcriptome to adapt to the cold weather in its distribution areas.

Rapid growth of Moso bamboo (Phyllostachys edulis): Cellular roadmaps, transcriptome dynamics, and environmental factors.

Moso bamboo (Phyllostachys edulis) shows remarkably rapid growth (114.5 cm/day), but the underlying biological mechanisms remain unclear. After examining more than 12,750 internodes from more than 510 culms from 17 Moso populations, we identified internode 18 as a representative internode for rapid growth. This internode includes a 2-cm cell division zone (DZ), a cell elongation zone up to 12 cm, and a secondary cell wall (SCW) thickening zone. These zones elongated 11.8 cm, produced approximately 570,000,000 cells, and deposited ∼28 mg g-1 dry weight (DW) lignin and ∼44 mg g-1 DW cellulose daily, far exceeding vegetative growth observed in other plants. We used anatomical, mathematical, physiological, and genomic data to characterize development and transcriptional networks during rapid growth in internode 18. Our results suggest that (1) gibberellin may directly trigger the rapid growth of Moso shoots, (2) decreased cytokinin and increased auxin accumulation may trigger cell DZ elongation, and (3) abscisic acid and mechanical pressure may stimulate rapid SCW thickening via MYB83L. We conclude that internode length involves a possible tradeoff mediated by mechanical pressure caused by rapid growth, possibly influenced by environmental temperature and regulated by genes related to cell division and elongation. Our results provide insight into the rapid growth of Moso bamboo.

Genome-Wide Identification, Expansion, and Evolution Analysis of Homeobox Gene Family Reveals TALE Genes Important for Secondary Cell Wall Biosynthesis in Moso Bamboo (Phyllostachys edulis).

The TALE gene family is a subfamily of the homeobox gene family and has been implicated in regulating plant secondary growth. However, reports about the evolutionary history and function of the TALE gene family in bamboo are limited. Here, the homeobox gene families of moso bamboo Olyra latifolia and Bonia amplexicaulis were identified and compared. Many duplication events and obvious expansions were found in the TALE family of woody bamboo. PhTALEs were found to have high syntenies with TALE genes in rice. Through gene co-expression analysis and quantitative real-time PCR analysis, the candidate PhTALEs were thought to be involved in regulating secondary cell wall development of moso bamboo during the fast-growing stage. Among these candidate PhTALEs, orthologs of OsKNAT7, OSH15, and SH5 in moso bamboo may regulate xylan synthesis by regulating the expression of IRX-like genes. These results suggested that PhTALEs may participate in the secondary cell wall deposition in internodes during the fast-growing stage of moso bamboo. The expansion of the TALE gene family may be implicated in the increased lignification of woody bamboo when divergent from herbaceous bamboos.