Abstract
Vegetative leaves in Arabidopsis are classified as either juvenile leaves or adult leaves based on their specific traits, such as leaf shape and the presence of abaxial trichomes. The timing of the juvenile-to-adult phase transition during vegetative development, called the vegetative phase change, is a critical decision for plants, as this transition is associated with crop yield, stress responses, and immune responses. Juvenile leaves are characterized by high levels of miR156/157, and adult leaves are characterized by high levels of miR156/157 targets, SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factors. The discovery of this miR156/157-SPL module provided a critical tool for elucidating the complex regulation of the juvenile-to-adult phase transition in plants. In this review, we discuss how the traits of juvenile leaves and adult leaves are determined by the miR156/157-SPL module and how different factors, including embryonic regulators, sugar, meristem regulators, hormones, and epigenetic proteins are involved in controlling the juvenile-to-adult phase transition, focusing on recent insights into vegetative phase change. We also highlight outstanding questions in the field that need further investigation. Understanding how vegetative phase change is regulated would provide a basis for manipulating agricultural traits under various conditions.
Highlights
Plants have two major stages of development, vegetative and reproductive, with distinct lateral structures, leaves and flowers, produced at each stage [1,2,3]
The vegetative phase itself is further divided into the juvenile phase and adult phase, since many “heteroblastic” traits of leaves, such as morphology, initiation rate, length/width ratio, size, leaf base angle, gibberellic acid sensitivity, vascular system complexity, and trichome growth vary as the shoot matures [1,2,3]
A role for jasmonic acid (JA) in vegetative phase change is suggested by the direct interaction of SPL9 with JA ZIM domain (JAZ) proteins that are involved in herbivore defense [12]
Summary
Plants have two major stages of development, vegetative and reproductive, with distinct lateral structures, leaves and flowers, produced at each stage [1,2,3]. Arabidopsis ectopically expressing juvenile phase markers produces more lateral roots, is more tolerant to salinity and drought stress, and is more resistant to herbivores, while rice ectopically expressing adult phase markers possesses an ideal plant architecture that improves grain yield (more grains per panicle) and immunity to fungus Magnaporthe oryzae [11,12,13,14,15,16,17] The variety of these developmental functions and physiological responses highlight the importance of understanding the mechanisms that control vegetative phase change and the potential to harness this knowledge to enhance agriculture. Plants overexpressing a non-cleavable miR156-target mimic (MIM156), which reduces the activity of miR156, did not produce any juvenile leaves after germination [10] These data strongly suggest that miR156 acts as a key regulator for vegetative phase change with decreased expression of miR156 associated with the transition from the juvenile to the adult phase.
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