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

A historical stepping-stone path for an island-colonizing cactus across a submerged "bridge" archipelago

Here we use population genomic data (ddRAD-Seq) and ecological niche modeling to test biogeographic hypotheses for the divergence of the island-endemic cactus species Cereus insularis Hemsl. (Cereeae; Cactaceae) from its sister species C. fernambucensis Lem. The Cereus insularis grows in the Fernando de Noronha Islands (FNI), a Neotropical archipelago located 350 km off the Brazilian Atlantic Forest (BAF) coast. Phylogeographic reconstructions support a northward expansion by the common ancestor of C. insularis and C. fernambucensis along the mainland BAF coast, with C. insularis diverging from the widespread mainland taxon C. fernambucensis after colonizing FNI in the late Pleistocene. The morphologically distinct C. insularis is monophyletic and nested within C. fernambucensis, as expected from a progenitor-derivative speciation model. We tested alternative biogeographic and demographic hypotheses for the colonization of the FNI using Approximate Bayesian Computation. We found the greatest support for a stepping-stone path that emerged during periods of decreased sea level (the "bridge" hypothesis), in congruence with historical ecological niche modeling that shows highly suitable habitats on stepping-stone islands during glacial periods. The outlier analyses reveal signatures of selection in C. insularis, suggesting a putative role of adaptation driving rapid anagenic differentiation of this species in FNI.

MdIPT1, an adenylate isopentenyltransferase coding gene from Malus domestica, is involved in branching and flowering regulation

Flowering and shoot branching are significant agricultural traits for apple tree breeding. Cytokinin metabolism and signaling pathways play a crucial role in plant development. However, little is known about cytokinin biosynthetic molecular mechanism and function involved in apple flowering and branching. In this study, an adenylate isopentenyl transferase coding gene MdIPT1, homologous to AtIPT3/AtIPT5 in Arabidopsis thaliana, was identified. MdIPT1 was highly expressed in apple floral and axillary buds and was dramatically up-regulated during floral induction and axillary bud outgrowth. The promoter of MdIPT1 showed high activity in multiple tissues and responded to different hormone treatments. The MdIPT1-overexpressing Arabidopsis showed a multi-branching and early-flowering phenotype, with elevated endogenous cytokinin levels and altered expression of genes related to branching and flower formation. Overexpression of MdIPT1 confers the growth vigor of transgenic apple callus on a CKs-deficient medium. Our findings suggest that MdIPT1 is a positive regulator involved in branching and flowering. The data presented herein provide extensive research results on MdIPT1 and will contribute to molecular breeding for new apple varieties.

Genome-Wide Identification and Expression Analysis of Isopentenyl transferase Family Genes during Development and Resistance to Abiotic Stresses in Tea Plant (Camellia sinensis)

The tea plant is an important economic crop and is widely cultivated. Isopentenyl transferase (IPT) is the first and rate-limiting enzyme of cytokinin (CK) signaling, which plays key roles in plant development and abiotic stress. However, the IPT gene family in tea plants has not been systematically investigated until now. The phylogenetic analyses, gene structures, and conserved domains were predicted here. The results showed that a total of 13 CsIPT members were identified from a tea plant genome database and phylogenetically classified into four groups. Furthermore, 10 CsIPT members belonged to plant ADP/ATP-IPT genes, and 3 CsIPTs were tRNA-IPT genes. There is a conserved putative ATP/GTP-binding site (P-loop motif) in all the CsIPT sequences. Based on publicly available transcriptome data as well as through RNA-seq and qRT-PCR analysis, the CsIPT genes which play key roles in the development of different tissues were identified, respectively. Furthermore, CsIPT6.2 may be involved in the response to different light treatments. CsIPT6.4 may play a key role during the dormancy and flush of the lateral buds. CsIPT5.1 may play important regulatory roles during the development of the lateral bud, leaf, and flower. CsIPT5.2 and CsIPT6.2 may both play key roles for increased resistance to cold-stress, whereas CsIPT3.2 may play a key role in improving resistance to high-temperature stress as well as drought-stress and rewatering. This study could provide a reference for further studies of CsIPT family’s functions and could contribute to tea molecular breeding.

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.

Overexpression of ZmIPT2 gene delays leaf senescence and improves grain yield in maize

Cytokinins (CTKs) are a major phytohormone group that are significant in the promotion of cellular division, growth, and divergence. Isopentenyl transferase (IPT) regulates a rate-limiting step in plant CTK synthesis, promotes the synthesis of isopentenyl adenonucleotides from 5-AMP and isopentenyl pyrophosphate, and then converts both these chemicals into various CTKs. Here, the full-length cDNA of ZmIPT2, which encodes 322 amino acids, was isolated and was introduced into a maize inbred line by Agrobacterium-mediated transformation. In both controlled environments and field experiments, the overexpression of ZmIPT2 gene in the transformed plants delayed leaf senescence. Compared to the receptor line, the transgenic maize lines retained higher chlorophyll levels, photosynthetic rates, and cytokinin content for an extended period of time, and produced significantly higher grain yield by a margin of 17.71-20.29% under normal field planting conditions. Subsequently, ten possible genes that interacted with ZmIPT2 were analyzed by qRT-PCR, showing that the expression pattern of GRMZM2G022904 was consistent with ZmIPT2 expression. Through comprehensive analysis, we screened for transgenic lines with stable inheritance of ZmIPT2 gene, clear functional efficiency, and significant yield improvement, in order to provide theoretical basis and material support for the breeding of new high-yield transgenic maize varieties.