The flattened and needlelike leaves of the pine family (Pinaceae) share a conserved genetic network for adaxial-abaxial
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RESEARCH ARTICLE
Open Access
The flattened and needlelike leaves of the pine family (Pinaceae) share a conserved genetic network for adaxial-abaxial polarity but have diverged for photosynthetic adaptation Hong Du1, Jin-Hua Ran1,2, Yuan-Yuan Feng1,2 and Xiao-Quan Wang1,2*
Abstract Background: Leaves have highly diverse morphologies. However, with an evolutionary history of approximately 200 million years, leaves of the pine family are relatively monotonous and often collectively called “needles”, although they vary in length, width and cross-section shapes. It would be of great interest to determine whether Pinaceae leaves share similar morpho-physiological features and even consistent developmental and adaptive mechanisms. Results: Based on a detailed morpho-anatomical study of leaves from all 11 Pinaceae genera, we particularly investigated the expression patterns of adaxial-abaxial polarity genes in two types of leaves (needlelike and flattened) and compared their photosynthetic capacities. We found that the two types of leaves share conserved spatial patterning of vasculatures and genetic networks for adaxial-abaxial polarity, although they display different anatomical structures in the mesophyll tissue differentiation and distribution direction. In addition, the species with needlelike leaves exhibited better photosynthetic capacity than the species with flattened leaves. Conclusions: Our study provides the first evidence for the existence of a conserved genetic module controlling adaxial-abaxial polarity in the development of different Pinaceae leaves. Keywords: Pinaceae, Leaf anatomy, Adaxial-abaxial polarity, Polarity gene, Developmental mechanism, Adaptive evolution, Photosynthesis
Background Most extant genera of conifers, the largest lineage of gymnosperms, originated in the middle and late Mesozoic, while a majority of extant species recently diverged until the Neogene and are now widely distributed throughout the world except Antarctica [1–4]. Conifers * Correspondence: [email protected] 1 State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, the Chinese Academy of Sciences, 20 Nanxincun, Xiangshan, Beijing 100093, China 2 University of Chinese Academy of Sciences, Beijing 100049, China
are characterized by their distinct leaves, i.e., “needles”, which underwent convergent or parallel evolution over a long history to adapt to different environments, and these leaves show two main types, needlelike and flattened leaves (including scale-like leaves). Generally, needlelike leaves appear to be more drought-resistant than flattened leaves [5, 6]. Previous studies on conifer “needles” have evaluated their morphology and physiology [7–9] but rarely focused on their developmental mechanisms and evolution. Pinaceae (the pine family),
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