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Vernalization and the chilling requirement to exit bud dormancy: shared or separate regulation?

Brunner AM, Evans LM, Hsu CY, Sheng X - Front Plant Sci (2014)

Bottom Line: Both gene function and association genetics studies in Populus are beginning to answer this question.We review Populus seasonal shoot development related to dormancy release and the floral transition and evidence for FT/TFL1-mediated regulation of these processes to consider the question of regulatory overlap.In addition, we discuss the potential for and challenges to integrating functional and population genomics studies to uncover the regulatory mechanisms underpinning these processes in woody plant systems.

View Article: PubMed Central - PubMed

Affiliation: Department of Forest Resources and Environmental Conservation, Virginia Polytechnic Institute and State University Blacksburg, VA, USA.

ABSTRACT
Similarities have long been recognized between vernalization, the prolonged exposure to cold temperatures that promotes the floral transition in many plants, and the chilling requirement to release bud dormancy in woody plants of temperate climates. In both cases the extended chilling period occurring during winter is used to coordinate developmental events to the appropriate seasonal time. However, whether or not these processes share common regulatory components and molecular mechanisms remain largely unknown. Both gene function and association genetics studies in Populus are beginning to answer this question. In Populus, studies have revealed that orthologs of the antagonistic flowering time genes FT and CEN/TFL1 might have central roles in both processes. We review Populus seasonal shoot development related to dormancy release and the floral transition and evidence for FT/TFL1-mediated regulation of these processes to consider the question of regulatory overlap. In addition, we discuss the potential for and challenges to integrating functional and population genomics studies to uncover the regulatory mechanisms underpinning these processes in woody plant systems.

No MeSH data available.


Related in: MedlinePlus

Winter to spring shoot development and roles of FT1, FT2, and CEN1 in Populus. (A) Seasonal shoot phenology and FT1, FT2, and CEN1 expression associated with dormancy release and the initiation of flowering. Seasonal phenology and relative gene expression patterns are based on study of adult Populus deltoides in Mississippi, USA (Yuceer et al., 2003; Hsu et al., 2011) with the exception of the timing of dormancy release, which is an estimate based on the apparent correlation between increasing FT1 expression and dormancy release in controlled environment studies reported by Rinne et al. (2011). The blue dotted line indicates that the shoot apex sample used for expression studies included leaf primordia smaller than 1 mm (e.g., LPL in the dormant bud). Note that the diagrams are not to scale and the number of EPL in a bud can be several more than the depicted number. In addition, an inflorescence typically forms more than 100 flowers that develop within the inflorescence bud over the course of the growing season and after winter dormancy, anthesis occurs the following spring. (B) Conceptual model of how seasonal changes in levels of FT1, CEN1, and FT2 sequentially contribute to the regulation of dormancy release, meristem identity and growth. AM, axillary meristem; IM, inflorescence meristem; FM, floral meristem; VM, vegetative meristem; EPL, early preformed leaves; EPS, early preformed shoot; LPL, late preformed leaves; NL, neoformed leaves; Br, bracts.
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Figure 1: Winter to spring shoot development and roles of FT1, FT2, and CEN1 in Populus. (A) Seasonal shoot phenology and FT1, FT2, and CEN1 expression associated with dormancy release and the initiation of flowering. Seasonal phenology and relative gene expression patterns are based on study of adult Populus deltoides in Mississippi, USA (Yuceer et al., 2003; Hsu et al., 2011) with the exception of the timing of dormancy release, which is an estimate based on the apparent correlation between increasing FT1 expression and dormancy release in controlled environment studies reported by Rinne et al. (2011). The blue dotted line indicates that the shoot apex sample used for expression studies included leaf primordia smaller than 1 mm (e.g., LPL in the dormant bud). Note that the diagrams are not to scale and the number of EPL in a bud can be several more than the depicted number. In addition, an inflorescence typically forms more than 100 flowers that develop within the inflorescence bud over the course of the growing season and after winter dormancy, anthesis occurs the following spring. (B) Conceptual model of how seasonal changes in levels of FT1, CEN1, and FT2 sequentially contribute to the regulation of dormancy release, meristem identity and growth. AM, axillary meristem; IM, inflorescence meristem; FM, floral meristem; VM, vegetative meristem; EPL, early preformed leaves; EPS, early preformed shoot; LPL, late preformed leaves; NL, neoformed leaves; Br, bracts.

Mentions: In Populus, both vegetative and floral shoot development proceeds acropetally. A dormant vegetative bud contains several preformed leaves that can be described as embryonic leaves/early preformed leaves (EPLs) or leaf primordia/late preformed leaves (LPLs) based on size, presence of trichomes and differentiation of blade and petiole (Critchfield, 1960; Yuceer et al., 2003; Figure 1A). In addition, meristematic domes have already formed in the axils of EPLs (Yuceer et al., 2003). The chilling sum needed to release dormancy varies with genotype, but dormancy is typically released several weeks prior to bud flush, whose timing is primarily determined by accumulated heat units (Cooke et al., 2012). Dormancy is released gradually and dormancy depth can be monitored by moving ramets at regular intervals to growth-promoting conditions and monitoring the time to bud flush or other features related to growth resumption. In Populus, apical meristems remain vegetative. In adult trees, some axillary meristems transition to inflorescence meristems that subsequently initiate bracts and then floral meristems in the bract axils (Brunner, 2010). Axillary inflorescence buds are microscopically distinguishable from axillary vegetative buds a few weeks after vegetative bud flush, when they begin to elongate and initiate bracts (Boes and Strauss, 1994; Yuceer et al., 2003). The development of the newly initiated inflorescence buds continues during the growing season and floral organ differentiation is mostly completed within the bud before winter dormancy. Inflorescence bud flush occurs before vegetative bud flush the following year. However, dormancy release of inflorescence buds has not been studied in Populus; thus, this review is limited to vegetative bud flush and the transition of some of the vegetative shoot’s axillary meristems to flowering. Populus exhibits an indeterminate growth pattern in that vegetative shoots will continue to elongate, initiating new leaves [neoformed leaves (NLs)] until the critical daylength for growth cessation occurs as long as other conditions are suitable for growth. However, as trees increase in size/age, the proportion of shoots that exhibit indeterminate growth decreases and a tree contains shoots ranging from determinate (short shoots with only preformed leaves) to fully indeterminate shoots (Critchfield, 1960). Moreover, inflorescence buds are most frequently present on determinate shoots or shoots that initiate only a few NLs (Yuceer et al., 2003; Brunner, 2010). A detailed seasonal time course study in Populus deltoides indicated that only meristems in the axils of LPLs can transition to flowering (i.e., convert to inflorescence meristems; Yuceer et al., 2003), whereas axillary meristems of EPL and NL are vegetative. Thus, in adult trees, there is a seasonal window where certain axillary meristems are able to transition to inflorescence meristems. The developmental state of the leaf and/or its axillary meristem could be factors in determining competency for the floral transition.


Vernalization and the chilling requirement to exit bud dormancy: shared or separate regulation?

Brunner AM, Evans LM, Hsu CY, Sheng X - Front Plant Sci (2014)

Winter to spring shoot development and roles of FT1, FT2, and CEN1 in Populus. (A) Seasonal shoot phenology and FT1, FT2, and CEN1 expression associated with dormancy release and the initiation of flowering. Seasonal phenology and relative gene expression patterns are based on study of adult Populus deltoides in Mississippi, USA (Yuceer et al., 2003; Hsu et al., 2011) with the exception of the timing of dormancy release, which is an estimate based on the apparent correlation between increasing FT1 expression and dormancy release in controlled environment studies reported by Rinne et al. (2011). The blue dotted line indicates that the shoot apex sample used for expression studies included leaf primordia smaller than 1 mm (e.g., LPL in the dormant bud). Note that the diagrams are not to scale and the number of EPL in a bud can be several more than the depicted number. In addition, an inflorescence typically forms more than 100 flowers that develop within the inflorescence bud over the course of the growing season and after winter dormancy, anthesis occurs the following spring. (B) Conceptual model of how seasonal changes in levels of FT1, CEN1, and FT2 sequentially contribute to the regulation of dormancy release, meristem identity and growth. AM, axillary meristem; IM, inflorescence meristem; FM, floral meristem; VM, vegetative meristem; EPL, early preformed leaves; EPS, early preformed shoot; LPL, late preformed leaves; NL, neoformed leaves; Br, bracts.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4269124&req=5

Figure 1: Winter to spring shoot development and roles of FT1, FT2, and CEN1 in Populus. (A) Seasonal shoot phenology and FT1, FT2, and CEN1 expression associated with dormancy release and the initiation of flowering. Seasonal phenology and relative gene expression patterns are based on study of adult Populus deltoides in Mississippi, USA (Yuceer et al., 2003; Hsu et al., 2011) with the exception of the timing of dormancy release, which is an estimate based on the apparent correlation between increasing FT1 expression and dormancy release in controlled environment studies reported by Rinne et al. (2011). The blue dotted line indicates that the shoot apex sample used for expression studies included leaf primordia smaller than 1 mm (e.g., LPL in the dormant bud). Note that the diagrams are not to scale and the number of EPL in a bud can be several more than the depicted number. In addition, an inflorescence typically forms more than 100 flowers that develop within the inflorescence bud over the course of the growing season and after winter dormancy, anthesis occurs the following spring. (B) Conceptual model of how seasonal changes in levels of FT1, CEN1, and FT2 sequentially contribute to the regulation of dormancy release, meristem identity and growth. AM, axillary meristem; IM, inflorescence meristem; FM, floral meristem; VM, vegetative meristem; EPL, early preformed leaves; EPS, early preformed shoot; LPL, late preformed leaves; NL, neoformed leaves; Br, bracts.
Mentions: In Populus, both vegetative and floral shoot development proceeds acropetally. A dormant vegetative bud contains several preformed leaves that can be described as embryonic leaves/early preformed leaves (EPLs) or leaf primordia/late preformed leaves (LPLs) based on size, presence of trichomes and differentiation of blade and petiole (Critchfield, 1960; Yuceer et al., 2003; Figure 1A). In addition, meristematic domes have already formed in the axils of EPLs (Yuceer et al., 2003). The chilling sum needed to release dormancy varies with genotype, but dormancy is typically released several weeks prior to bud flush, whose timing is primarily determined by accumulated heat units (Cooke et al., 2012). Dormancy is released gradually and dormancy depth can be monitored by moving ramets at regular intervals to growth-promoting conditions and monitoring the time to bud flush or other features related to growth resumption. In Populus, apical meristems remain vegetative. In adult trees, some axillary meristems transition to inflorescence meristems that subsequently initiate bracts and then floral meristems in the bract axils (Brunner, 2010). Axillary inflorescence buds are microscopically distinguishable from axillary vegetative buds a few weeks after vegetative bud flush, when they begin to elongate and initiate bracts (Boes and Strauss, 1994; Yuceer et al., 2003). The development of the newly initiated inflorescence buds continues during the growing season and floral organ differentiation is mostly completed within the bud before winter dormancy. Inflorescence bud flush occurs before vegetative bud flush the following year. However, dormancy release of inflorescence buds has not been studied in Populus; thus, this review is limited to vegetative bud flush and the transition of some of the vegetative shoot’s axillary meristems to flowering. Populus exhibits an indeterminate growth pattern in that vegetative shoots will continue to elongate, initiating new leaves [neoformed leaves (NLs)] until the critical daylength for growth cessation occurs as long as other conditions are suitable for growth. However, as trees increase in size/age, the proportion of shoots that exhibit indeterminate growth decreases and a tree contains shoots ranging from determinate (short shoots with only preformed leaves) to fully indeterminate shoots (Critchfield, 1960). Moreover, inflorescence buds are most frequently present on determinate shoots or shoots that initiate only a few NLs (Yuceer et al., 2003; Brunner, 2010). A detailed seasonal time course study in Populus deltoides indicated that only meristems in the axils of LPLs can transition to flowering (i.e., convert to inflorescence meristems; Yuceer et al., 2003), whereas axillary meristems of EPL and NL are vegetative. Thus, in adult trees, there is a seasonal window where certain axillary meristems are able to transition to inflorescence meristems. The developmental state of the leaf and/or its axillary meristem could be factors in determining competency for the floral transition.

Bottom Line: Both gene function and association genetics studies in Populus are beginning to answer this question.We review Populus seasonal shoot development related to dormancy release and the floral transition and evidence for FT/TFL1-mediated regulation of these processes to consider the question of regulatory overlap.In addition, we discuss the potential for and challenges to integrating functional and population genomics studies to uncover the regulatory mechanisms underpinning these processes in woody plant systems.

View Article: PubMed Central - PubMed

Affiliation: Department of Forest Resources and Environmental Conservation, Virginia Polytechnic Institute and State University Blacksburg, VA, USA.

ABSTRACT
Similarities have long been recognized between vernalization, the prolonged exposure to cold temperatures that promotes the floral transition in many plants, and the chilling requirement to release bud dormancy in woody plants of temperate climates. In both cases the extended chilling period occurring during winter is used to coordinate developmental events to the appropriate seasonal time. However, whether or not these processes share common regulatory components and molecular mechanisms remain largely unknown. Both gene function and association genetics studies in Populus are beginning to answer this question. In Populus, studies have revealed that orthologs of the antagonistic flowering time genes FT and CEN/TFL1 might have central roles in both processes. We review Populus seasonal shoot development related to dormancy release and the floral transition and evidence for FT/TFL1-mediated regulation of these processes to consider the question of regulatory overlap. In addition, we discuss the potential for and challenges to integrating functional and population genomics studies to uncover the regulatory mechanisms underpinning these processes in woody plant systems.

No MeSH data available.


Related in: MedlinePlus