The plant growth cycle, from germination to flowering and seed formation, is controlled by a complex network of key genes that regulate development, hormone activity, and environmental responses. These genes help plants grow, reproduce, and adapt to changes in light, temperature, and nutrients.
Here are the main groups and examples of important genes involved in different stages of the plant growth cycle:
Seed Germination and Early Growth Genes
These genes help seeds break dormancy and begin active growth when conditions are suitable.
• ABI3 (Abscisic Acid Insensitive 3): Controls seed dormancy through abscisic acid (ABA) signaling. High ABA activates ABI3 to prevent germination under unfavorable conditions.
• GAI and RGA (GA Insensitive and Repressor of GA): Repress gibberellin (GA) activity. When GA levels rise, these repressors degrade, allowing the seed to germinate.
• LEC1 and LEC2 (Leafy Cotyledon 1 and 2): Regulate embryo development and seed maturation.
• DELLA proteins: Inhibit GA responses; their breakdown promotes germination and stem growth.
Vegetative Growth and Development Genes
These genes regulate root, stem, and leaf growth during the vegetative phase.
• WOX (Wuschel-related Homeobox): Maintains stem cells in shoot and root meristems for continuous organ formation.
• KNOX (Knotted1-like Homeobox): Controls shoot development and leaf formation by balancing cytokinin and GA levels.
• SCR (Scarecrow) and SHR (Short Root): Determine root structure and patterning.
• YABBY and HD-ZIP genes: Define leaf shape, polarity, and structure.
Flowering and Reproductive Phase Genes
These genes control the switch from vegetative to reproductive growth and the formation of flowers.
• FT (Flowering Locus T): Acts as the “florigen” gene that moves from leaves to the shoot apex to trigger flowering.
• FLC (Flowering Locus C): Acts as a repressor that delays flowering; its expression is reduced by cold exposure (vernalization).
• SOC1 (Suppressor of Overexpression of Constans 1): Integrates signals from light, temperature, and hormones to initiate flowering.
• CO (Constans): Controls flowering in response to day length; activates FT under long days.
• AP1 (Apetala1) and LFY (Leafy): Determine floral meristem identity and start flower organ development.
• AG (Agamous): Controls the formation of stamens and carpels.
Hormone Signaling Genes
Plant hormones coordinate all stages of growth, and these genes regulate their action.
• AUX/IAA and ARF (Auxin Response Factor): Regulate auxin-related processes like cell elongation and root formation.
• GA20ox and GA3ox: Control gibberellin synthesis for stem elongation and flowering.
• ARR (Arabidopsis Response Regulators): Mediate cytokinin signaling for cell division and shoot growth.
• ETR and EIN2 (Ethylene Response and Ethylene Insensitive 2): Control ethylene responses such as fruit ripening and leaf fall.
• PYR/PYL/RCAR: Function as ABA receptors that regulate stress response and seed dormancy.
Temperature and Environmental Response Genes
These genes help plants adjust their growth to environmental conditions.
• VRN1 and VRN2 (Vernalization Genes): Control flowering in cereals like wheat and barley after cold exposure.
• CBF (C-Repeat Binding Factor): Regulates genes for cold tolerance.
• PIF (Phytochrome Interacting Factor): Coordinates plant responses to light and temperature, influencing germination and flowering.
Senescence and Maturation Genes
These genes control the final stage of plant growth, including leaf aging, nutrient recycling, and fruit ripening.
• SAG (Senescence-Associated Genes): Regulate aging and nutrient movement from old to young tissues.
• NAC and WRKY transcription factors: Control leaf senescence and stress-induced aging.
• RIN (Ripening Inhibitor): Regulates fruit ripening in plants such as tomato by controlling ethylene production and color changes.
In summary, plant growth is regulated by a network of genes that interact with hormones and environmental cues. Each group of genes has a specific role—from seed germination and vegetative growth to flowering and maturation. Together, they ensure that plants grow efficiently, reproduce successfully, and adapt to changing conditions throughout their life cycle.