Expression of IPT in Asakura-sanshoo (Zanthoxylum piperitum (L.) DC. f. inerme Makino) Alters Tree Architecture, Delays Leaf Senescence, and Changes Leaf Essential Oil Composition

Interaction of Phytohormones and External Environmental Factors in the Regulation of the Bud Dormancy in Woody Plants

Bud dormancy and release are essential phenomena that greatly assist in adapting to adverse growing conditions and promoting the holistic growth and development of perennial plants. The dormancy and release process of buds in temperate perennial trees involves complex interactions between physiological and biochemical processes influenced by various environmental factors, representing a meticulously orchestrated life cycle. In this review, we summarize the role of phytohormones and their crosstalk in the establishment and release of bud dormancy. External environmental factors, such as light and temperature, play a crucial role in regulating bud germination. We also highlight the mechanisms of how light and temperature are involved in the regulation of bud dormancy by modulating phytohormones. Moreover, the role of nutrient factors, including sugar, in regulating bud dormancy is also discussed. This review provides a foundation for enhancing our understanding of plant growth and development patterns, fostering agricultural production, and exploring plant adaptive responses to adversity.

Expression and functional analysis of CsA-IPT5 splice variants during shoot branching in Camellia sinensis

Alternative splicing (AS) is a process by which several functional splice variants are generated from the same precursor mRNA. In our recent study, five CsA-IPT5 splice variants with various numbers of ATTTA motifs in the untranslated regions (UTRs) were cloned. Meanwhile, their transient expression, as well as the expression and functional analysis in the two shoot branching processes were studied. Here, we examined how these splice variants regulate the other three important shoot branching processes, including the spring tea development, the distal branching of new shoots, and the shoot branching induced by 2,3,5-triiodobenzoic acid (TIBA) spraying, and thus unraveling the key CsA-IPT5 transcripts which play the most important roles in the shoot branching of tea plants. The results showed that the increased expression of 5' UTR AS3, 3' UTR AS1 and 3' UTR AS2 could contribute to the increased synthesis of tZ/iP-type cytokinins (CKs), thus promoting the spring tea development. Meanwhile, in the TIBA-induced shoot branching or in the distal branching of the new shoots, CsA-IPT5 transcripts regulated the synthesis of CsA-IPT5 protein and CKs through transcriptional regulation of the ratios of its splice variants. Moreover, 3' UTR AS1 and 3' UTR AS2 both play key roles in these two processes. In summary, it is revealed that 3' UTR AS1 and 3' UTR AS2 of CsA-IPT5 might act as the predominant splice variants in shoot branching of the tea plant, and they both can serve as gene resources for tea plant breeding.

Genome-Wide Identification and Analysis of the Growth-Regulating Factor Family in Zanthoxylum armatum DC and Functional Analysis of ZaGRF6 in Leaf Size and Longevity Regulation

Growth-regulating factors (GRFs) are plant-specific transcription factors that play an important role in plant growth and development. In this study, fifteen GRF gene members containing QLQ and WRC domains were identified in Zanthoxylum armatum. Phylogenetic and collinearity analysis showed that ZaGRFs were closely related to CsGRFs and AtGRFs, and distantly related to OsGRFs. There are a large number of cis-acting elements related to hormone response and stress induction in the GRF gene promoter region of Z. armatum. Tissue-specific expression analysis showed that except for ZaGRF7, all the ZaGRFs were highly expressed in young parts with active growth and development, including terminal buds, seeds, and young flowers, suggesting their key roles in Z. armatum growth and development. Eight ZaGRFs were selected to investigate the transcriptional response to auxin, gibberellin and drought treatments. A total of six ZaGRFs in the NAA treatment, four ZaGRFs in the GA₃ treatment, and six ZaGRFs in the PEG treatment were induced and significantly up-regulated. Overexpression of ZaGRF6 increased branching and chlorophyll content and delayed senescence of transgenic Nicotiana benthamiana. ZaGRF6 increased the expression of CRF2 and suppressed the expression of ARR4 and CKX1, indicating that ZaGRF6 is involved in cytokinin metabolism and signal transduction. These research results lay a foundation for further analysis of the GRF gene function of Z. armatum and provide candidate genes for growth, development, and stress resistance breeding of Z. armatum.

A novel adenylate isopentenyltransferase 5 regulates shoot branching via the ATTTA motif in Camellia sinensis

BACKGROUND

Shoot branching is one of the important agronomic traits affecting yields and quality of tea plant (Camellia sinensis). Cytokinins (CTKs) play critical roles in regulating shoot branching. However, whether and how differently alternative splicing (AS) variant of CTKs-related genes can influence shoot branching of tea plant is still not fully elucidated.

RESULTS

In this study, five AS variants of CTK biosynthetic gene adenylate isopentenyltransferase (CsA-IPT5) with different 3' untranslated region (3' UTR) and 5' UTR from tea plant were cloned and investigated for their regulatory effects. Transient expression assays showed that there were significant negative correlations between CsA-IPT5 protein expression, mRNA expression of CsA-IPT5 AS variants and the number of ATTTA motifs, respectively. Shoot branching processes induced by exogenous 6-BA or pruning were studied, where CsA-IPT5 was demonstrated to regulate protein synthesis of CsA-IPT5, as well as the biosynthesis of trans-zeatin (tZ)- and isopentenyladenine (iP)-CTKs, through transcriptionally changing ratios of its five AS variants in these processes. Furthermore, the 3' UTR AS variant 2 (3AS2) might act as the predominant AS transcript.

CONCLUSIONS

Together, our results indicate that 3AS2 of the CsA-IPT5 gene is potential in regulating shoot branching of tea plant and provides a gene resource for improving the plant-type of woody plants.

A Genotypic Comparison Reveals That the Improvement in Nitrogen Remobilization Efficiency in Oilseed Rape Leaves Is Related to Specific Patterns of Senescence-Associated Protease Activities and Phytohormones

Oilseed rape (Brassica napus L.) is an oleoproteaginous crop characterized by low N use efficiency (NUE) that is mainly related to a weak Nitrogen Remobilization Efficiency (NRE) during the sequential leaf senescence of the vegetative stages. Based on the hypothesis that proteolysis efficiency is crucial for the improvement of leafNRE, our objective was to characterize key senescence-associated proteolytic mechanisms of two genotypes (Ténor and Samouraï) previously identified with contrasting NREs. To reach this goal, biochemical changes, protease activities and phytohormone patterns were studied in mature leaves undergoing senescence in two genotypes with contrasting NRE cultivated in a greenhouse under limiting or ample nitrate supply. The genotype with the higher NRE (Ténor) possessed enhanced senescence processes in response to nitrate limitation, and this led to greater degradation of soluble proteins compared to the other genotype (Samouraï). This efficient proteolysis is associated with (i) an increase in serine and cysteine protease (CP) activities and (ii) the appearance of new CP activities (RD21-like, SAG12-like, RD19-like, cathepsin-B, XBCP3-like and aleurain-like proteases) during senescence induced by N limitation. Compared to Samouraï, Ténor has a higher hormonal ratio ([salicylic acid] + [abscisic acid])/([cytokinins]) that promotes senescence, particularly under low N conditions, and this is correlated with the stronger protein degradation and serine/CP activities observed during senescence. Short statement: The improvement in N recycling during leaf senescence in a genotype of Brassica napus L. characterized by a high nitrogen remobilization efficiency is related to a high phytohormonal ratio ([salicylic acid] + [abscisic acid])/([cytokinins]) that promotes leaf senescence and is correlated with an increase or the induction of specific serine and cysteine protease activities.

Exogenous application of GA3 inactively regulates axillary bud outgrowth by influencing of branching-inhibitors and bud-regulating hormones in apple (Malus domestica Borkh.)

Although gibberellin (GA) has been reported to control branching, little is known about how GA mediates signals regulating the outgrowth of axillary buds (ABs). In the current study, the effect of the exogenous application of 5.0 mM GA₃ on ABs outgrowth on 1-year-old 'Nagafu No. 2'/T337/M. robusta Rehd. apple trees was investigated and compared to the bud-activating treatments, 5 mM BA or decapitation. Additionally, the expression of genes related to bud-regulating signals and sucrose levels in ABs was examined. Results indicated that GA₃ did not promote ABs' outgrowth, nor down-regulate the expression of branching repressors [MdTCP40, MdTCP33, and MdTCP16 (homologs of BRANCHED1 and BRC2)], which were significantly inhibited by the BA and decapitation treatments. MdSBP12 and MdSBP18, the putative transcriptional activators of these genes, which are expressed at lower levels in BA-treated and decapitated buds, were up-regulated in the GA₃ treatment in comparison to the BA treatment. Additionally, GA₃ did not up-regulate the expression of CK response- and auxin transport-related genes, which were immediately induced by the BA treatment. In addition, GA₃ also up-regulated the expression of several Tre6P biosynthesis genes and reduced sucrose levels in ABs. Sucrose levels, however, were still higher than what was observed in BA-treated buds, indicating that sucrose may not be limiting in GA₃-controlled AB outgrowth. Although GA₃ promoted cell division, it was not sufficient to induce AB outgrowth. Conclusively, some branching-inhibiting genes and bud-regulating hormones are associated with the inability of GA₃ to activate AB outgrowth.

Identification and expression analysis of the IPT and CKX gene families during axillary bud outgrowth in apple (Malus domestica Borkh.)

Cytokinins (CKs) play a crucial role in promoting axillary bud outgrowth and targeting the control of CK metabolism can be used to enhance branching in plants. CK levels are maintained mainly by CK biosynthesis (isopentenyl transferase, IPT) and degradation (dehydrogenase, CKX) genes in plants. A systematic study of the IPT and CKX gene families in apple, however, has not been conducted. In the present study, 12 MdIPTs and 12 MdCKXs were identified in the apple genome. Systematic phylogenetic, structural, and synteny analyses were performed. Expression analysis of these genes in different tissues was also assessed. MdIPT and MdCKX genes exhibit distinct expression patterns in different tissues. The response of MdIPT, MdCKX, and MdPIN1 genes to various treatments (6-BA, decapitation and Lovastatin, an inhibitor of CKs synthesis) that impact branching were also investigated. Results indicated that most of the MdIPT and MdCKX, and MdPIN1 genes were upregulated by 6-BA and decapitation treatment, but inhibited by Lovastatin, a compound that effectively suppresses axillary bud outgrowth induced by decapitation. These findings suggest that cytokinin biosynthesis is required for the activation of bud break and the export of auxin from buds in apple tree with intact primary shoot apex or decapitated apple tree. MdCKX8 and MdCKX10, however, exhibited little response to decapitation, but were significantly up-regulated by 6-BA and Lovastatin, a finding that warrants further investigation in order to understand their function in bud-outgrowth.

Proteomic Investigations of Proteases Involved in Cotyledon Senescence: A Model to Explore the Genotypic Variability of Proteolysis Machinery Associated with Nitrogen Remobilization Efficiency during the Leaf Senescence of Oilseed Rape

Oilseed rape is characterized by a low nitrogen remobilization efficiency during leaf senescence, mainly due to a lack of proteolysis. Because cotyledons are subjected to senescence, it was hypothesized that contrasting protease activities between genotypes may be distinguishable early in the senescence of cotyledons. To verify this assumption, our goals were to (i) characterize protease activities in cotyledons between two genotypes with contrasting nitrogen remobilization efficiency (Ténor and Samouraï) under limiting or ample nitrate supply; and (ii) test the role of salicylic acid (SA) and abscisic acid (ABA) in proteolysis regulation. Protease activities were measured and identified by a proteomics approach combining activity-based protein profiling with LC-MS/MS. As in senescing leaves, chlorophyll and protein contents decrease in senescing cotyledons and are correlated with an increase in serine and cysteine protease activities. Two RD21-like and SAG-12 proteases previously associated with an efficient proteolysis in senescing leaves of Ténor are also detected in senescing cotyledons. The infiltration of ABA and SA provokes the induction of senescence and several cysteine and serine protease activities. The study of protease activities during the senescence of cotyledons seems to be a promising experimental model to investigate the regulation and genotypic variability of proteolysis associated with efficient N remobilization.