Elucidation of molecular and hormonal background of early growth cessation and endodormancy induction in two contrasting Populus hybrid cultivars

Abstract

Background Over the life cycle of perennial trees, the dormant state enables the avoidance of abiotic stress conditions. The growth cycle can be partitioned into induction, maintenance and release and is controlled by complex interactions between many endogenous and environmental factors. While phytohormones have long been linked with dormancy, there is increasing evidence of regulation by DAM and CBF genes. To reveal whether the expression kinetics of CBFs and their target PtDAM1 is related to growth cessation and endodormancy induction in Populus, two hybrid poplar cultivars were studied which had known differential responses to dormancy inducing conditions. Results Growth cessation, dormancy status and expression of six PtCBFs and PtDAM1 were analyzed. The ‘Okanese’ hybrid cultivar ceased growth rapidly, was able to reach endodormancy, and exhibited a significant increase of several PtCBF transcripts in the buds on the 10th day. The ‘Walker’ cultivar had delayed growth cessation, was unable to enter endodormancy, and showed much lower CBF expression in buds. Expression of PtDAM1 peaked on the 10th day only in the buds of ‘Okanese’. In addition, PtDAM1 was not expressed in the leaves of either cultivar while leaf CBFs expression pattern was several fold higher in ‘Walker’, peaking at day 1. Leaf phytohormones in both cultivars followed similar profiles during growth cessation but differentiated based on cytokinins which were largely reduced, while the Ox-IAA and iP7G increased in ‘Okanese’ compared to ‘Walker’. Surprisingly, ABA concentration was reduced in leaves of both cultivars. However, the metabolic deactivation product of ABA, phaseic acid, exhibited an early peak on the first day in ‘Okanese’. Conclusions Our results indicate that PtCBFs and PtDAM1 have differential kinetics and spatial localization which may be related to early growth cessation and endodormancy induction under the regime of low night temperature and short photoperiod in poplar. Unlike buds, PtCBFs and PtDAM1 expression levels in leaves were not associated with early growth cessation and dormancy induction under these conditions. Our study provides new evidence that the degradation of auxin and cytokinins in leaves may be an important regulatory point in a CBF-DAM induced endodormancy. Further investigation of other PtDAMs in bud tissue and a study of both growth-inhibiting and the degradation of growth-promoting phytohormones is warranted.

Transcriptomic Analysis Reveals the Positive Role of Abscisic Acid in Endodormancy Maintenance of Leaf Buds of Magnolia wufengensis

“…Additionally, eight PmCBFs were upregulated under the stimulus of a cold signal, which then induced the expression of all six DAM genes during dormancy development ( Zhang et al, 2018 ; Zhao et al, 2018a ). In the Populus hybrid, PtCBF1 and PtDAM1 induction was found to be related to ED development ( Boldizsár et al, 2021 ). In pear, Niu et al (2015) found that PpCBF can induce the expression of PpDAM and PpDAM and subsequently inhibit PpFT , which then stimulates growth cessation and promote dormancy maintenance.…”

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

“…Researchers have identified several physiological functions of GA in the release of dormancy in plants: (1) The primary physiological function of GA is to promote plant growth, specifically cell elongation. Studies have demonstrated that treating dwarf plants with GA has a positive impact on growth, specifically focusing on promoting internode elongation [88].…”

“…The bud primordium absorbs nutrients and grows into new branches or remains dormant. Dormancy is the temporary suspension of visible growth of any meristematic plant structure, and it occurs during the annual growth cycle of most temperate woody plants, including Pinus, Cupressaceae, and dicotyledons [1][2][3]. Bud dormancy manifests in both terminal and lateral buds of plants, triggered by the synergistic effects of shortened daylight hours and lower temperatures in late autumn, as an adaptive response to prepare for the impending cold winter season [4][5][6].…”