Abstract
BackgroundLeaves 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.ResultsBased 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.ConclusionsOur study provides the first evidence for the existence of a conserved genetic module controlling adaxial-abaxial polarity in the development of different Pinaceae leaves.
Highlights
Morphological and anatomical divergence of Pinaceae leaves Based on the width/thickness ratio (WTR) of the cross section, Pinaceae leaves could be mainly divided into two types, needlelike and flattened (Fig. 1a and Additional file 1: Figure S1)
Anatomical observation by scanning electron microscopy (SEM) indicated that the two types of leaves in Pinaceae each have distinct structural characteristics
In this study, based on a detailed morpho-anatomical study of leaves from all 11 Pinaceae genera, the expression patterns of adaxial-abaxial polarity genes were investigated in the delimited needlelike and flattened leaves of this family
Summary
Angiosperm leaves develop as bifacial structures with distinct adaxial and abaxial identities, which enables the maximum photosynthetic rate [15,16,17,18]. The mutually antagonistic interactions between the adaxial and abaxial identity regulators determine the dorsoventrally flattened structure of conventional bifacial leaves. A kind of unifacial leaf exists in angiosperms, which is characterized by only an abaxialized identity usually with a radially symmetric, cylindrical structure [30,31,32]. It is intriguing to explore when the molecular genetic mechanism for specifying leaf adaxial-abaxial polarity originated, whether conifer “needles” are regulated by this mechanism and whether this mechanism is conserved between the needlelike and flattened leaves in conifers. With the development of high-throughput sequencing technologies, several genomes of gymnosperms, especially Pinaceae, have been released [12,13,14, 33], providing a good opportunity to disentangle how Pinaceae leaves genetically developed to different types
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