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Summary Pits are regions in the cell walls of plant tracheary elements that lack secondary walls. Each pit consists of a space within the secondary wall called a pit chamber, and a modified primary wall called the pit membrane. The pit membrane facilitates transport of solutions between vessel cells and restricts embolisms during drought. Here we analyzed the role of an angiosperm‐specific TPX2‐like microtubule protein MAP20 in pit formation usingBrachypodium distachyonas a model system.Live cell imaging was used to analyze the interaction of MAP20 with microtubules and the impact of MAP20 on microtubule dynamics. MAP20‐specific antibody was used to study expression and localization of MAP20 in different cell types during vascular bundle development. We used an artificial microRNAs (amiRNA) knockdown approach to determine the function ofMAP20.MAP20 is expressed during the late stages of vascular bundle development and localizes around forming pits and under secondary cell wall thickenings in metaxylem cells. MAP20 suppresses microtubule depolymerization; however, unlike the animal TPX2 counterpart, MAP20 does not cooperate with the γ‐tubulin ring complex in microtubule nucleation. Knockdown ofMAP20causes bigger pits, thinner pit membranes, perturbed vasculature development, lower reproductive potential and higher drought susceptibility.We conclude thatMAP20may contribute to drought adaptation by modulating pit size and pit membrane thickness in metaxylem.
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Necrotic upper tips1 mimics heat and drought stress and encodes a protoxylem-specific transcription factor in maize
Maintaining sufficient water transport during flowering is essential for proper organ growth, fertilization, and yield. Water deficits that coincide with flowering result in leaf wilting, necrosis, tassel browning, and sterility, a stress condition known as “tassel blasting.” We identified a mutant, necrotic upper tips1 ( nut1 ), that mimics tassel blasting and drought stress and reveals the genetic mechanisms underlying these processes. The nut1 phenotype is evident only after the floral transition, and the mutants have difficulty moving water as shown by dye uptake and movement assays. These defects are correlated with reduced protoxylem vessel thickness that indirectly affects metaxylem cell wall integrity and function in the mutant. nut1 is caused by an Ac transposon insertion into the coding region of a unique NAC transcription factor within the VND clade of Arabidopsis . NUT1 localizes to the developing protoxylem of root, stem, and leaf sheath, but not metaxylem, and its expression is induced by flowering. NUT1 downstream target genes function in cell wall biosynthesis, apoptosis, and maintenance of xylem cell wall thickness and strength. These results show that maintaining protoxylem vessel integrity during periods of high water movement requires the expression of specialized, dynamically regulated transcription factors within the vasculature.
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- PAR ID:
- 10200154
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 117
- Issue:
- 34
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- 20908 to 20919
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1073/pnas.2005014117
