Comparison of phytohormone levels and transcript profiles during seasonal dormancy transitions in underground adventitious buds of leafy spurge

Authors: Chao, Wun; Dogramaci, Munevver; Horvath, David; Anderson, James; Foley, Michael

Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2017
Publication Date: 5/27/2017
Citation: Chao, W.S., Dogramaci, M., Horvath, D.P., Anderson, J.V., Foley, M.E. 2017. Comparison of phytohormone levels and transcript profiles during seasonal dormancy transitions in underground adventitious buds of leafy spurge. Plant Molecular Biology. 94(3):281-302.

Interpretive Summary: Leafy spurge (Euphorbia esula L.) is an herbaceous weed that maintains a perennial growth habit through seasonal production of abundant underground adventitious buds (UABs) on the crown and lateral roots. Leafy spurge UABs are capable of manifesting the three well-defined phases of para-, endo-, and ecodormancy. Paradormancy is growth cessation controlled by physiological factors external to the affected meristems, endodormacy is growth cessation controlled by internal physiological factors, and ecodormancy is growth cessation controlled by external environmental factors. In this study, phytohormone abundance and the transcriptomes were compared during seasonal dormancy transitions in UABs of leafy spurge based on hormone profiling and RNA-seq analyses. Our results showed that different phytohormone signals acted in concert to induce UABs into the three phases of dormancy; in addition, extended cold treatment may trigger physiological stress in endodormant buds, and that these stress-associated signals induced the endo- to ecodormancy transition and growth competence.

Technical Abstract: Leafy spurge (Euphorbia esula L.) is an herbaceous perennial weed that maintains its perennial growth habit through generation of underground adventitious buds (UABs) on the crown and lateral roots. These UABs undergo seasonal phases of dormancy under natural conditions, namely para-, endo-, and ecodormancy in summer, fall, and winter, respectively. These dormancy phases can also be induced in growth chambers by manipulating photoperiod and temperature. In this study, UABs induced into the three phases of dormancy under controlled conditions were used to compare changes in phytohormone and transcriptome profiles. Results indicated that relatively high levels of ABA, the ABA metabolite PA, and IAA were found in paradormant buds. When UABs transitioned from para- to endodormancy, ABA and PA levels decreased, whereas IAA levels were maintained. Additionally, transcript profiles associated with regulation of soluble sugars and ethylene activities were also increased during para- to endodormancy transition, which may play some role in maintaining endodormancy status. When crown buds transitioned from endo- to ecodormancy, the ABA metabolites PA and DPA decreased significantly along with the down-regulation of ABA biosynthesis genes, ABA2 and NCED3. IAA levels were also significantly lower in ecodormant buds than that of endodormant buds. We hypothesize that extended cold treatment may trigger physiological stress in endodormant buds, and that these stress-associated signals induced the endo- to ecodormancy transition and growth competence. The up-regulation of NAD/NADH phosphorylation and dephosphorylation pathway, and MAF3-like and GRFs genes, may be considered as markers of growth competency.