The association of hormone signalling genes, transcription and changes in shoot anatomy during moso bamboo growth

Abstract

Moso bamboo is a large, woody bamboo with the highest ecological, economic and cultural value of all the bamboo types and accounts for up to 70% of the total area of bamboo grown. However, the spatiotemporal variation role of moso bamboo shoot during growth period is still unclear. We found that the bamboo shoot growth can be divided into three distinct periods, including winter growth, early growth and late growth based on gene expression and anatomy. In the early growth period, lateral buds germinated from the top of the bamboo joint in the shoot tip. Intercalary meristems grew vigorously during the winter growth period and early growth period, but in the late growth period, mitosis in the intercalary meristems decreased. The expression of cell cycle-associated genes and the quantity of differentially expressed genes were higher in early growth than those in late growth, appearing to be influenced by hormonal concentrations. Gene expression analysis indicates that hormone signalling genes play key roles in shoot growth, while auxin signalling genes play a central role. In situ hybridization analyses illustrate how auxin signalling genes regulate apical dominance, meristem maintenance and lateral bud development. Our study provides a vivid picture of the dynamic changes in anatomy and gene expression during shoot growth in moso bamboo, and how hormone signalling-associated genes participate in moso bamboo shoot growth.

Keywords: endogenous hormone; fast growth; hormone signalling genes; moso bamboo; shoot anatomy.

Figure 1

Examples of moso bamboo shoots in seven growth stages (a–g represented for S1–S7). Bars, 1 cm (a); 15 cm (b); 30 cm (c); 1 m (d); 1.5 m (e); 3 m (f); and 4 m (g).

Figure 2

Daily height variation (a) and daily height increments of bamboo shoots (b). The horizontal axis represents the survey date, and vertical axis represents the shoot height (a) and height increment per day (b), respectively.

Figure 3

Transverse section of moso bamboo shoot tips in seven growth stages (S1–S7). (h–k) Apical meristems of S1, S3, S4 and S6. Bars, 2 mm (a–g); 500 μm (h–k). L is lateral bud, I is internode, B is bamboo joint, A is apical bud, V is vascular bundle, S is bamboo sheath and P is pith.

Figure 4

Cross‐sections and longitudinal sections of tissue from developing shoots (the fifth internode) in seven growth stages (S1–S7). (a–g) Cross‐sections of the fifth internode. Bars, 200 μm. (h–n) Longitudinal sections of the fifth internode. Bars, 500 μm. E, G, P, S and V represent epidermis, ground tissues, pith, bamboo sheath and vascular bundles, respectively.

Figure 5

Internal structure of moso bamboo shoot cells (a, d) S1 stage, (b, e) S4 stage, (c, f) S6 stage. The N, M, F and S represent nucleolus, mitochondria, fat droplets and starch grains, respectively.

Figure 6

Dynamic changes in the concentration of five endogenous hormones in moso bamboo shoots at different developmental stages and internodes: abscisic acid (ABA) (a), brassinolide (Br) (b), indole acetic acid (IAA) (c), gibberellic acid (GA ₃) (d) and zeatin riboside (ZR) (e). Different letters on a column with the same pattern indicate significant differences at P ≤ 0.05 according to an LSD test. In a–e, the horizontal axis represents the growth stage, and the vertical axis represents the endogenous hormone content (ng/FW). (f) The ratio between ZR, BR, GA ₃ and IAA and ABA at different growth stages.

Figure 7

(a) Transcriptome relationships among different samples. (b) Expression of genes in eight samples. The x‐axis and y‐axis in each chart represent gene quantity and the eight growth stages, respectively.

Figure 8

Differentially expressed genes related to shoot elongation. (a) Statistical graph of differentially expressed transcripts at seven developmental stages. (b) Overlapping sets of induced transcripts in seven different growth stages. (c) Overlapping sets of repressed transcripts in seven different growth stages.

Figure 9

Verification of DGEs by qRT‐PCR. The relative amount of mRNA (y‐axis) is a ratio normalized by TIP41 (tonoplast intrinsic protein 41). The shoot growth stages are on the x‐axis. R indicates the correlation coefficient for the expression between RNA‐Seq and qRT‐PCR data. The expression of each gene in CK was arbitrarily set at 1.0.

Figure 10

GO terms that were significantly enriched (FDR <0.05) in the DGEs (a) GO component, (b) GO function, (c) GO biological process.

Figure 11

The average expression of plant hormone signalling‐related gene families at different growth stages. The number in the heat map represents different expression clusters. The colour scale represents log2‐transformed RPKM (reads per kilobase per million) values. Green indicates low expression, and red indicates high expression.

Figure 12

A co‐expression network of differentially expressed hormone signalling genes in moso bamboo.

Figure 13

The expression of auxin signalling‐related genes in moso bamboo shoots at different growth stages. S1, S4, S6, B represents winter bamboo shoot, 3 m height shoot, 9 m height shoot and lateral buds, S represents the expression of the sense probe in in situ hybridization. Arrowheads point to transcript accumulation. A, B, E, G, P, S and V represent the apical bud, lateral bud, epidermis, ground tissues, pith, bamboo sheath and vascular bundle, respectively. Bars, 2 mm. (a) PH01000025G1600 (AUX/IAA), (b) PH01000046G0220 (ARF), (c) H01000373G0290 (AUX/LAX), (d) PH01001098G0440 (AUX/IAA).