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The superior photosynthetic efficiency of C 4 leaves over C 3 leaves is owing to their unique Kranz anatomy, in which the vein is surrounded by one layer of bundle sheath (BS) cells and one layer of mesophyll (M) cells. Kranz anatomy development starts from three contiguous ground meristem (GM) cells, but its regulators and underlying molecular mechanism are largely unknown. To identify the regulators, we obtained the transcriptomes of 11 maize embryonic leaf cell types from five stages of pre-Kranz cells starting from median GM cells and six stages of pre-M cells starting from undifferentiated cells. Principal component and clustering analyses of transcriptomic data revealed rapid pre-Kranz cell differentiation in the first two stages but slow differentiation in the last three stages, suggesting early Kranz cell fate determination. In contrast, pre-M cells exhibit a more prolonged transcriptional differentiation process. Differential gene expression and coexpression analyses identified gene coexpression modules, one of which included 3 auxin transporter and 18 transcription factor (TF) genes, including known regulators of Kranz anatomy and/or vascular development. In situ hybridization of 11 TF genes validated their expression in early Kranz development. We determined the binding motifs of 15 TFs, predicted TF target gene relationships among the 18 TF and 3 auxin transporter genes, and validated 67 predictions by electrophoresis mobility shift assay. From these data, we constructed a gene regulatory network for Kranz development. Our study sheds light on the regulation of early maize leaf development and provides candidate leaf development regulators for future study.
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A fossil dicranid moss from the Late Cretaceous of Antarctica
An anatomically preserved moss gametophyte has been discovered in a marine carbonate concretion from the Baculites Hill locality, James Ross Island, Antarctica. The concretion is derived from the Late Cretaceous Beta Member of the Santa Marta Formation, dated as early to middle Campanian (ca. 80 Ma). The moss has actinomorphic stems with alternate branching, spiral, patent leaf arrangement and large numbers of attached rhizoids. The largest stem is 210 mm in diameter with the largest branch measuring up to 3.7 mm long and 90–100 mm wide. Most stems appear to contain a distinct conducting strand. Cross sections show that the leaves are strongly plicate with a simple D-shaped costal anatomy and unistratose laminae typically with bistratose margins. Leaves range from 650–700 mm wide and at least 700 mm long. The costa appears percurrent, 90 mm wide and 55 mm thick. Laminar cells are elongate, rhomboidal, L/W ¼ 5:1. No ornamentation or papillae have been observed on the upper medial cells of the leaf. These fossils show leaf morphology and costal anatomy similar to several orders of acrocarpous mosses, in the Dicranidae including species of the family Rhabdoweisiaceae. While the combination of characters does not fit into any known genus, it suggests that this moss represents a fossil member of the Dicranales s.l. To date, this represents the most completely preserved moss gametophyte from Gondwana.
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- Award ID(s):
- 1953993
- PAR ID:
- 10552219
- Publisher / Repository:
- The American Bryological and Lichenological Society
- Date Published:
- Journal Name:
- The Bryologist
- Volume:
- 127
- Issue:
- 3
- ISSN:
- 0007-2745
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1639/0007-2745-127.3.342
