A gene regulatory network for tiller development mediated by Tin8 in maize

The complex gene regulatory network underlying maize tiller development remains largely unknown. Here we identified two major quantitative trait loci (QTLs) for tiller number, Tin8 on chromosome 8 and the previously known Tb1 on chromosome 1, in a population derived from a teosinte–maize cross. Map-based cloning and association mapping revealed that Tin8 corresponding to Zcn8 encoding a PEBP-related kinase, is down-regulated in transcription and thus results in decreased tiller number. Strong interaction between Tin8 and the key gen Tb1 was detected for tiller number. Further RNA-seq analysis showed that the expressions of 13 genes related to tiller development were controlled by Tin8. Our results support the existence of a complex gene regulatory network for the outgrowth of maize tiller bud, in which Zcn8 controls 13 tiller-related genes including four genes for hormonal responses. Especially, Zcn8 represses Gt1, D14 and Tru1, through the interaction of Tb1.

OsSPL14/17 are required for phosphate-deficiency-inhibited tiller bud outgrowth by repression of PIN2 in rice

Phosphorus (P) is an essential nutrient for food crops. P-deficiency inhibits tiller development of rice; thus, an understanding of the P-modulated tiller development mechanism is crucial for grain yield. Auxin and strigolactones (SLs) have been implicated as regulators of tiller formation in rice. However, the relationships between the two are unclear. We found that low-P (LP) inhibited rice tiller formation and tiller bud elongation, with higher levels of SLs. In contrast to wild-type (WT) plants, the number of tillers was greater in d10 (SL biosynthesis mutant), d14, and d53 (SL-responsive mutants) under LP conditions, demonstrating that D53 participates in LP- mediated inhibition of rice tiller formation. The strong interaction between D53 and SPL14/17 inhibited their transcriptional activities under normal P (NP) conditions, and mutation of SPL14/17 eliminated their inhibitory effects on tiller formation under LP conditions. SPL14/17 inhibited transcriptional from the PIN2 promoter, and overexpression of PIN2 induced tiller development under LP conditions. Therefore, binding of D53 to SPL14/17 represses their transcriptional inhibition, reversing SPL14/17-inhibited PIN2 transcription and promoting tiller development under NP conditions. Proteasomal degradation of D53 releases SPL14/17, thus repressing PIN2 transcription and preventing induction of tillering under LP conditions.

Nitrogen Attenuated Zinc-Mediated Promotion of Rice Tillering Under Low Temperature via Regulating Auxin and Cytokinin Balance

Background and aims Zinc (Zn) can improve rice resistance to abiotic stress and participate in IAA synthesis. The absorption of Zn is closely related to nitrogen (N) nutrition. However, little is known about the mechanisms by which Zn regulates rice low-temperature resistance and tillering recovery after low-temperature under different N levels. Methods Water culture experiment was conducted with two temperatures (22°C and 12°C), two N levels (1.43 mM and 2.86 mM NH4NO3), and three Zn levels (0.08 µM, 0.15 µM and 0.30 µM ZnSO4·7H2O). Results Low-temperature decreased rice tillering, which was further exacerbated at high N levels. Increasing Zn application could improve rice low-temperature resistance under normal N levels, enhance nutrient absorption, improve tiller bud cytokinin (CTK) concentration and CTK/IAA ratio, finally accelerate tillering recovery one week before normal Zn treatment. High N attenuated the contribution of Zn under low temperature, but moderate Zn was beneficial to tillering recovery by regulating the balance of tiller bud IAA and CTK concentration, and IAA transport. Conclusions Increasing Zn application improved rice tolerance to low-temperature stress and promoted tillering recovery, which was aggravated under high N levels. However, appropriate Zn application under high N level was conducive to breaking tiller dormancy and promoting tillering growth spurts when recovering to a normal temperature, which was related to the hormone balance and nutrient absorption synergistic regulation by N and Zn.

Characterization of full-length transcriptome in Saccharum officinarum and molecular insights into tiller development

Background Although extensive breeding efforts are ongoing in sugarcane (Saccharum officinarum L.), the average yield is far below the theoretical potential. Tillering is an important component of sugarcane yield, however, the molecular mechanism underlying tiller development is still elusive. The limited genomic data in sugarcane, particularly due to its complex and large genome, has hindered in-depth molecular studies. Results Herein, we generated full-length (FL) transcriptome from developing leaf and tiller bud samples based on PacBio Iso-Seq. In addition, we performed RNA-seq from tiller bud samples at three developmental stages (T0, T1 and T2) to uncover key genes and biological pathways involved in sugarcane tiller development. In total, 30,360 and 20,088 high-quality non-redundant isoforms were identified in leaf and tiller bud samples, respectively, representing 41,109 unique isoforms in sugarcane. Likewise, we identified 1063 and 1037 alternative splicing events identified in leaf and tiller bud samples, respectively. We predicted the presence of coding sequence for 40,343 isoforms, 98% of which was successfully annotated. Comparison with previous FL transcriptomes in sugarcane revealed 2963 unreported isoforms. In addition, we characterized 14,946 SSRs from 11,700 transcripts and 310 lncRNAs. By integrating RNA-seq with the FL transcriptome, 468 and 57 differentially expressed genes (DEG) were identified in T1vsT0 and T2vsT0, respectively. Strong up-regulation of several pyruvate phosphate dikinase and phosphoenolpyruvate carboxylase genes suggests enhanced carbon fixation and protein synthesis to facilitate tiller growth. Similarly, up-regulation of linoleate 9S-lipoxygenase and lipoxygenase genes in the linoleic acid metabolism pathway suggests high synthesis of key oxylipins involved in tiller growth and development. Conclusions Collectively, we have enriched the genomic data available in sugarcane and provided candidate genes for manipulating tiller formation and development, towards productivity enhancement in sugarcane.

Regulation of 2,4-D Isooctyl Ester on Triticum aestivum and Aegilops tauschii Tillering and Endogenous Phytohormonal Responses

Tillering is an important agronomic trait essential for the yield of Triticum aestivum and the propagation of Aegilops tauschii. However, the effect of phytohormones on T. aestivum and Ae. tauschii tillering and the underlying regulatory mechanisms remain poorly understood. In the study, we found that T. aestivum and Ae. tauschii exhibited different tillering sensitivities to the auxin herbicide 2,4-D isooctyl ester. At 3 days post-application, tiller bud growth was inhibited by 77.50% in T. aestivum, corresponding to 2.0-fold greater inhibition than that in Ae. tauschii (38.71%). Transcriptome analysis showed that differentially expressed genes (DEGs) in the T. aestivum response to 2,4-D isooctyl ester were mainly enriched in plant hormone metabolism and signal transduction pathways, but similar changes were not observed in Ae. tauschii. Among that, the auxin biosynthesis and signaling induced by 2,4-D isooctyl ester was quite different between the two species. A total of nine candidate genes involved in varied tillering responses were selected from the DEGs and validated by quantitative real-time PCR. Endogenous hormone levels were assayed to further verify the RNA-seq results. After 2,4-D isooctyl ester treatment, a significant increase in abscisic acid (ABA) levels was observed in T. aestivum, whereas ABA levels were relatively stable in Ae. tauschii. The herbicide induced more cytokinin (CTK) accumulation in Ae. tauschii than in T. aestivum. External ABA clearly restricted tiller bud growth in both T. aestivum and Ae. tauschii, while 6-benzyl aminopurine had no significant effect. These results indicate that ABA and CTK may be related with 2,4-D isooctyl ester-regulated tillering differences between the two species, which will help to further understand the mechanism of the auxin-mediated regulation of tillering

Temporal-spatial changes in the belowground bud bank in interdune lowlands of an active sand dune ecosystem in northeastern China

Aims The belowground bud bank plays an important role in vegetation restoration of sand dune ecosystems in semi-arid regions. However, few studies have focused on the temporal-spatial changes of belowground bud banks in interdune lowlands. Methods The size and composition of belowground bud bank in five interdune lowlands with different sizes were investigated for one growing season to determine the temporal and spatial changes in belowground bud bank. Important Findings Total bud bank density was the highest in the medium-sized interdune lowland as was tiller bud density. The density of stem-base buds exhibited an opposite trend while rhizome bud density did not change with interdune lowland size. There was a significant seasonal change in the bud bank size. The total bud density peaked in August and was the lowest in October. A similar trend was found for rhizome bud density, whereas the density of stem-base buds showed an opposite trend, and tiller bud density did not change significantly during the growing season. We conclude that the belowground bud bank density is changed with interdune lowland size and season. These results contribute to the understanding of adaptive strategies of plants growing in active dune ecosystems and provide pointers for adopting effective measures to restore and conserve dune vegetation in semi-arid regions.