Florigen governs shoot regeneration

A group of CLE peptides regulates de novo shoot regeneration in Arabidopsis thaliana

Known for their regulatory roles in stem cell homeostasis, CLAVATA3/ESR-RELATED (CLE) peptides also function as mediators of external stimuli such as hormones. De novo shoot regeneration, representing the remarkable plant cellular plasticity, involves reconstitution of stem cells under control of stem-cell regulators. Yet whether and how stem cell-regulating CLE peptides are implicated in plant regeneration remains unknown. By CRISPR/Cas9-induced loss-of-function studies, peptide application, precursor overexpression, and expression analyses, the role of CLE1-CLE7 peptides and their receptors in de novo shoot regeneration was studied in Arabidopsis thaliana. CLE1-CLE7 are induced by callus-induction medium and dynamically expressed in pluripotent callus. Exogenously-applied CLE1-CLE7 peptides or precursor overexpression effectively leads to shoot regeneration suppression, whereas their simultaneous mutation results in enhanced regenerative capacity, demonstrating that CLE1-CLE7 peptides redundantly function as negative regulators of de novo shoot regeneration. CLE1-CLE7-mediated shoot regeneration suppression is impaired in loss-of-function mutants of callus-expressed CLAVATA1 (CLV1) and BARELY ANY MERISTEM1 (BAM1) genes, indicating that CLV1/BAM1 are required for CLE1-CLE7-mediated shoot regeneration signaling. CLE1-CLE7 signaling resulted in transcriptional repression of WUSCHEL (WUS), a stem cell-promoting transcription factor known as a principal regulator of plant regeneration. Our results indicate that functionally-redundant CLE1-CLE7 peptides genetically act through CLV1/BAM1 receptors and repress WUS expression to modulate shoot-regeneration capacity, establishing the mechanistic basis for CLE1-CLE7-mediated shoot regeneration and a novel role for CLE peptides in hormone-dependent developmental plasticity.

Micropropagation from Inflorescence Nodal Segments of Phalaenopsis and Acclimatization of Plantlets Using Different Substrates

Phalaenopsis is an orchid genus of great economic value in world floriculture. In vitro clonal propagation is the only large-scale feasible method for Phalaenopsis propagation, but it is difficult because of the low multiplication rate. The aim of this study was to evaluate the effect of types and concentrations of N6-benzyladenine (6-BA) and gibberellic acid (GA3) on the in vitro multiplication of shoots from inflorescence nodal segments (INS) of Phalaenopsis hybrids. INS with one axillary bud were inoculated in New Dogashima Medium with different combinations of BA and GA3. The results show that the treatment containing 1.0 mg L−1 BA and 1.5 mg L−1 GA3 showed the higher percentage of live inflorescence segments (71.48%) and a number of shoots (1.68 shoots/INS). The highest 6-BA concentration (4 mg L−1) tested in this study resulted in the best shoot multiplication rate (4.3). Contamination and browning of the INS tissues were the main difficulties identified for clonal propagation of Phalaenopsis. Successful in vitro rooting occurred on half-strength Murashige and Skoog medium (100%), and acclimatization (100%) was obtained independent of the substrates. However, the best gains in number of roots, leaves, chlorophyll content, and fresh weight of plantlets were achieved using vermiculite.

Sex and Regeneration

Regeneration is usually regarded as a unique plant or some animal species process. In reality, regeneration is a ubiquitous process in all multicellular organisms. It ranges from response to wounding by healing the wounded tissue to whole body neoforming (remaking of the new body). In a larger context, regeneration is one facet of two reproduction schemes that dominate the evolution of life. Multicellular organisms can propagate their genes asexually or sexually. Here I present the view that the ability to regenerate tissue or whole-body regeneration is also determined by the sexual state of the multicellular organisms (from simple animals such as hydra and planaria to plants and complex animals). The above idea is manifested here by showing evidence that many organisms, organs, or tissues show inhibited or diminished regeneration capacity when in reproductive status compared to organs or tissues in nonreproductive conditions or by exposure to sex hormones.