Brachypodium distachyon MAP20 functions in metaxylem pit development and contributes to drought recovery

Abstract

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 using Brachypodium distachyon as 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 of MAP20. 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 of MAP20 causes bigger pits, thinner pit membranes, perturbed vasculature development, lower reproductive potential and higher drought susceptibility. We conclude that MAP20 may contribute to drought adaptation by modulating pit size and pit membrane thickness in metaxylem.

The wild grass Brachypodium distachyon as a developmental model system

“…Importantly, most of the work we will describe would not have been possible without the resources described above. There are a number of additional developmental processes being studied in B. distachyon; important contributions include for example, cell wall biology (see Coomey et al, 2020) and references therein), vascular development (Sakai et al, 2021;Smertenko et al, 2019), pleiotropic genes like the NOOT-BOP-COCH-LIKE genes (Magne et al, 2020), seed germination (Wolny et al, 2018), species-specific aspects of abscission zone formation (Yu et al, 2020), and even thigmomorphogenesis-the developmental response to touch (Coomey et al, 2021). We apologize for not being able to cover all the developmental work done with B. distachyon due to space limitations.…”

Brachypodium: 20 years as a grass biology model system; the way forward?

“…The small B. distachyon genome encodes a surprisingly large number of GST (a similar number to wheat) and it may be that BdGSTF8, BdGSTU35, and BdGSTU42 were influencing the relative tolerance to osmotic stress [84]. A link between physiology and drought tolerance was made in B. distachyon when the microtubule protein MAP20 was shown to be important in the function of pits in the cell walls of plant tracheary elements Here, researchers worked initially on the hybrid aspen (Populus tremula × Populus tremuloides), but when investigating tMAP20 in an annual species, the functional genomic properties of B. distachyon proved to be useful [85]. Other studies have adopted Brachypodium for similar reasons to characterise common responses to a wide range of abiotic stresses; for example, mechanical stress [86], heat shock proteins [87], the cystatin protease family [88], or phospholipase C genes [89].…”

The microtubule-associated protein SlMAP70 interacts with SlIQD21 and regulates fruit shape formation in tomato

“…To determine the effect of SUN10/SlIQD21a and SlMAP70-1 expression on microtubule dynamics, time-lapse studies were performed using a frame-subtraction approach (Lindeboom et al, 2013; Smertenko et al, 2020). Here, microtubule growth (polymerization) was pseudocolored in red and microtubule shrinkage (depolymerization) were pseudocolored in cyan.…”