Molecular and physiological regulation of adventitious root formation in Petunia cuttings in response to nutrient supply and dark exposure
Final Report Abstract
Petunia hybrida was used to investigate the molecular physiological regulation behind the stimulation of AR formation in shoot tip cuttings in response to high versus low nitrogen supply to stock plants and to a temporary cold dark incubation (7 days, 10 °C) before the cuttings were planted and cultivated under light. Analysis of plant hormones, amino acids, activities of crucial enzymes and of the transcriptome were combined with pharmacological treatments and the use of mutants, while the cutting was considered as a functional system consisting of communicating source and sink units. The results indicate that the improved AR formation of cuttings of P. hybrida in response to dark exposure involves a coordinated proteolysisdriven mobilization of nitrogen sources in the cutting in terms of mobile amino acids and an invertase-driven enhancement of the sink activity in the stem base as rooting zone. As a result, sucrose and phloem-mobile amino acids, in particular asparagine and glutamine, are preferentially allocated to the rooting zone. Higher nitrogen content in cuttings also enhances the amino acid levels, while this effect is less strong than the dark effect. The data further provide evidence for the function of auxin homeostasis and polar auxin transport (PAT) in the dark response of rooting while this is expected to contribute to the root induction and sink establishment in the stem base. Under darkness, higher IAA levels are attained during the induction phase, which are further correlated with enhanced expression of PIN1 and components of the auxin signal machinery such as ARF8. SAUR proteins appeared as important new candidates for the implementation of auxin-mediated dark stimulation of AR formation. A higher early accumulation of jasmonic acid and late accumulation of abscisic acid may further contribute to the dark effect on AR formation. Application of a PAT blocker eliminated the promotive dark effect on AR formation. The decreased rooting of non-dark exposed cuttings versus dark exposed cuttings could be rescued by IAA application during the induction phase but only when the cuttings did not experience nitrogen deficiency. Additional findings that nitrogen deficiency in cuttings had only a marginal effect on the IAA levels in the stem base and did not impede the formation of root meristemoids but strongly inhibited differentiation of subsequent root primordia does not support a functional role of early auxin action in nitrogen-limited AR formation. Rooting phase-specific expression of AP2/ERF and GRAS-genes indicates important functions during AR formation in petunia under light. In vitro rooting studies with mutants deficient in biosynthesis or transport of strigolactones indicate an an inhibitory role of strigolactones in AR formation in petunia, which is not affected by a short dark treatment but subject to a cross-talk with sucrose. Together with the sequenced genome of two parental lines of P. hybrida and other tools available for petunia, the results provide an important new basis for the detailed analysis of gene function in environmentally mediated AR formation in cuttings.
Publications
- (2019) Efficient adventitious root formation in Petunia hybrida cuttings: when signals meet resources. Acta Hortic. (Acta Horticulturae) (1242) 917–926
Druege, U.; Klopotek, Y.; Zerche, S.; Hajirezaei, M.-R.; Yang, H.; Franken, P.
(See online at https://doi.org/10.17660/ActaHortic.2019.1242.134) - 2016. A higher sink competitiveness of the rooting zone and invertases are involved in dark stimulation of adventitious root formation in Petunia hybrida cuttings. Plant Science 243, 10–22
Klopotek, Y.; Franken, P.; Klaering, H.-P.; Fischer, K.; Hause, B.; Hajirezaei, M.; Druege, U.
(See online at https://doi.org/10.1016/j.plantsci.2015.11.001) - 2016. Insight into the evolution of the Solanaceae from the parental genomes of Petunia hybrida. Nature Plants 2, Article number: 1607
Bombarely, A.; Moser, M.; Amrad, A.; Bapaume, L.; Barry, C.S.; Bliek, M.; Boersma, M.R;. Borghi, L.; Bruggmann, R.; Bucher, M.; D'Agostino, N.; Druege, U.; Dudareva, N.; Egea-Cortines, M.; Delledonne, M.; Fernandez-Pozo, N.; Franken, P.; et al.
(See online at https://doi.org/10.1038/NPLANTS.2016.74) - 2016. Nitrogen remobilisation facilitates adventitious root formation on reversible dark-induced carbohydrate depletion in Petunia hybrida. BMC Plant Biology 16:219, 1-20
Zerche, S.; Haensch, K.-T.; Druege, U.; Hajirezaei, M.-R.
(See online at https://doi.org/10.1186/s12870-016-0901-6) - 2016. Plant hormone homeostasis, signaling, and function during adventitious root formation in cuttings. Frontiers in Plant Science 7: 381
Druege, U.; Franken, P.; Hajirezaei, M.
(See online at https://doi.org/10.3389/fpls.2016.00381)
