New Insights Into the Local Auxin Biosynthesis and Its Effects on the Rapid Growth of Moso Bamboo (Phyllostachys edulis)

Abstract

Auxin plays a crucial regulatory role in higher plants, but systematic studies on the location of auxin local biosynthesis are rare in bamboo and other graminaceous plants. We studied moso bamboo (Phyllostachys edulis), which can grow up to 1 m/day and serves as a reference species for bamboo and other fast-growing species. We selected young tissues such as root tips, shoot tips, young culm sheaths, sheath blades, and internode divisions for local auxin biosynthesis site analysis. IAA immunofluorescence localization revealed that auxin was similarly distributed in different stages of 50-cm and 300-cm bamboo shoots. Shoot tips had the highest auxin content, and it may be the main site of auxin biosynthesis in the early stage of rapid growth. A total of 22 key genes in the YUCCA family for auxin biosynthesis were identified by genome-wide identification, and these had obvious tissue-specific and spatio-temporal expression patterns. In situ hybridization analysis revealed that the localization of YUCCA genes was highly consistent with the distribution of auxin. Six major auxin synthesis genes, PheYUC3-1, PheYUC6-1, PheYUC6-3, PheYUC9-1, PheYUC9-2, and PheYUC7-3, were obtained that may have regulatory roles in auxin accumulation during moso bamboo growth. Culm sheaths were found to serve as the main local sites of auxin biosynthesis and the auxin required for internode elongation may be achieved mainly by auxin transport.

Keywords: YUCCA; auxin; culm sheaths; local biosynthesis; moso bamboo; rapid growth.

Figure 1

Structure of moso bamboo shoots with corresponding sampling tissues (A) 50-cm-height moso bamboo shoot, (B) sheath blade (the upper component of culm sheaths, the base is connected to the tip of sheath and is the metamorphic leaf of bamboo shoot), (C) bamboo shoot internode 1/5 from the tip, (D) young sheath wrapped shoot tip, (E) intact young sheath, (F) root tip (the tip of the bamboo root growing out of the base of the bamboo shoot). (A) Bar = 5 cm, (B–F) Bar = 1 cm.

Figure 2

IAA immunofluorescence localization. CR root tip (the tip of the bamboo root growing out of the base of the bamboo shoot), TS tip of shoot, SB sheath blade (the upper component of culm sheaths, the base is connected to the tip of sheath and is the metamorphic leaf of bamboo shoot), BI bamboo shoot internode 1/5 from the tip, and YS young sheath. Bar = 50 μm.

Figure 3

Auxin content of different tissues. CR root tip (the tip of the bamboo root growing out of the base of the bamboo shoot), TS tip of shoot, SB sheath blade (the upper component of culm sheaths, the base is connected to the tip of sheath and is the metamorphic leaf of bamboo shoot), BI bamboo shoot internode 1/5 from the tip, and YS young sheath. (A) Content of IAA; (B) Content of IAA-ASP (IAA-aspartate).

Figure 4

Phylogenetic tree and expression pattern analysis of YUCCA genes family. (A) Phylogenetic tree of 160 YUCCA genes of 14 species. Phe Phyllostachys edulis, AT Arabidopsis thaliana, Os Oryza sativa, evm Amborella trichopoda, Cucsa Cucumis sativus, Glyma Glycine max, Mapoly Marchantia polymorpha, Medtr Medicago truncatula, Pp Physcomitrella patens, Prupe Prunus persica, Potri Populus trichocarpa, Number Selaginella moellendorffii, Solyc Solanum lycopersicum, and Zm Zea mays. (B) Individual phylogenetic tree of 22 members of the moso bamboo YUCCA gene family. All genes were renamed with rice homology. Correspondence is shown in Supplementary Table S3. All trees are unrooted trees, and branch lengths represent only sequence differences. (C,D) Expression of different treatments and different growth stages (IAA Indole-3-acetic acid, NAA Naphthaleneacetic acid, TIBA Triiodobenzoic acid, and SUC Sucrose. WBS Winter bamboo shoots, 50 50-cm bamboo shoots, 100 100-cm bamboo shoots, 300 300-cm bamboo shoots, 600 600-cm bamboo shoots, 900 900-cm bamboo shoots, and 1,200 1,200-cm bamboo shoots). Spring bamboo shoots with good natural growth conditions and shoots 50 ± 2 cm tall were selected and injected with 20 μM IAA, 20 μM NAA, 200 μM TIBA, 200 μM SUC, and water 50 ml at the 5th internode and treated once every 3 days for a total of five times. Each treatment had 30 biological replicates. At the control shoot height of 4 m, the middle of the eighteenth node of each treatment was selected for analysis. The transcriptome data are available in the SAR database under the access number: PRJNA788576. The color scheme as in Log2 fold change relative to mock treatment.

Figure 5

Real-time quantitative PCR(qRT-PCR) analysis of YUCCA gene family. 1 PheYUC6-3, 2 PheYUC9-1, 3 PheYUC2, 4 PheYUC4-2, 5 PheYUC6-1, 6 PheYUC5, 7 PheYUC4-1, 8 PheYUC3-2, 9 PheYUC1-2, 10 PheYUC8-1, 11 PheYUC6-2, 12 PheYUC9-2, 13 PheYUC3-1, 14 PheYUC4-3, 15 PheYUC1-1, 16 PheYUC8-2, 17 PheYUC7-4, 18 PheYUC7-2, 19 PheYUC7-1, 20 PheYUC7-3, 21 PheYUC11, and 22 PheYUC6-4. The reference gene is TIP41 of moso bamboo, see Supplementary Table S4 for relevant primer information. CR root tip (the tip of the bamboo root growing out of the base of the bamboo shoot), TS tip of shoot, SB sheath blade (the upper component of culm sheaths, the base is connected to the tip of sheath and is the metamorphic leaf of bamboo shoot), BI bamboo shoot internode 1/5 from the tip, and YS young sheath.

Figure 6

In situ expression analysis of YUCCA genes in different tissues. (A,B) root, (C,D) shoot tip, (E,F) sheath blade, (G,H) bamboo shoot internode 1/5 from the tip, and (I,J) young sheath. Bar = 50 μm.