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Summary: Among many mRNA modifications, adenine methylation at the N6 position (N6‐methyladenosine, m6A) is known to affect mRNA biology extensively. The influence of m6A has yet to be assessed under drought, one of the most impactful abiotic stresses.We show that Arabidopsis thaliana (L.) Heynh. (Arabidopsis) plants lacking mRNA ADENOSINE METHYLASE (MTA) are drought‐sensitive. Subsequently, we comprehensively assess the impacts of MTA‐dependent m6A changes during drought on mRNA abundance, stability, and translation in Arabidopsis.During drought, there is a global trend toward hypermethylation of many protein‐coding transcripts that does not occur in mta. We also observe complex regulation of m6A at a transcript‐specific level, possibly reflecting compensation by other m6A components. Importantly, a subset of transcripts that are hypermethylated in an MTA‐dependent manner exhibited reduced turnover and translation in mta, compared with wild‐type (WT) plants, during drought. Additionally, MTA impacts transcript stability and translation independently of m6A. We also correlate drought‐associated deposition of m6A with increased translation of modulators of drought response, such as RD29A, COR47, COR413, ALDH2B, ERD7, and ABF4 in WT, which is impaired in mta.m6A is dynamic during drought and, alongside MTA, promotes tolerance by regulating drought‐responsive changes in transcript turnover and translation. [ABSTRACT FROM AUTHOR]

SUMMARY: Plasmodesmata (PD) are nanochannels that facilitate cell‐to‐cell transport in plants. More productive and photosynthetically efficient C4 plants form more PD at the mesophyll (M)‐bundle sheath (BS) interface in their leaves than their less efficient C3 relatives. In C4 leaves, PD play an essential role in facilitating the rapid metabolite exchange between the M and BS cells to operate a biochemical CO2 concentrating mechanism, which increases the CO2 partial pressure at the site of Rubisco in the BS cells and hence photosynthetic efficiency. The genetic mechanism controlling PD formation in C3 and C4 leaves is largely unknown, especially in monocot crops, due to the technical challenge of quantifying these nanostructures with electron microscopy. To address this issue, we have generated stably transformed lines of Oryza sativa (rice, C3) and Setaria viridis (setaria, C4) with fluorescent protein‐tagged PD to build the first spatiotemporal atlas of leaf pit field (cluster of PD) density in monocots without the need for electron microscopy. Across leaf development, setaria had consistently more PD connections at the M‐BS wall interface than rice while the difference in M‐M pit field density varied. While light was a critical trigger of PD formation, cell type and function determined leaf pit field density. Complementary temporal mRNA sequencing and gene co‐expression network analysis revealed that the pattern of pit field density correlated with differentially expressed PD‐associated genes and photosynthesis‐related genes. PD‐associated genes identified from our co‐expression network analysis are related to cell wall expansion, translation and chloroplast signalling. Significance Statement: The important roles of plasmodesmata (PD) in plant biology present opportunity to improve crop performance but need more knowledge on the genetic control of PD formation to be realised. Here, we use unique bioimaging tools to understand PD formation during monocot leaf development in the context of photosynthesis, and identify potential genes involved. [ABSTRACT FROM AUTHOR]

SUMMARY: Transcript stability is an important determinant of its abundance and, consequently, translational output. Transcript destabilisation can be rapid and is well suited for modulating the cellular response. However, it is unclear the extent to which RNA stability is altered under changing environmental conditions in plants. We previously hypothesised that recovery‐induced transcript destabilisation facilitated a phenomenon of rapid recovery gene downregulation (RRGD) in Arabidopsis thaliana (Arabidopsis) following light stress, based on mathematical calculations to account for ongoing transcription. Here, we test this hypothesis and investigate processes regulating transcript abundance and fate by quantifying changes in transcription, stability and translation before, during and after light stress. We adapt syringe infiltration to apply a transcriptional inhibitor to soil‐grown plants in combination with stress treatments. Compared with measurements in juvenile plants and cell culture, we find reduced stability across a range of transcripts encoding proteins involved in RNA binding and processing. We also observe light‐induced destabilisation of transcripts, followed by their stabilisation during recovery. We propose that this destabilisation facilitates RRGD, possibly in combination with transcriptional shut‐off that was confirmed for HSP101, ROF1 and GOLS1. We also show that translation remains highly dynamic over the course of light stress and recovery, with a bias towards transcript‐specific increases in ribosome association, independent of changes in total transcript abundance, after 30 min of light stress. Taken together, we provide evidence for the combinatorial regulation of transcription and stability that occurs to coordinate translation during light stress and recovery in Arabidopsis. Significance Statement: We provide a method for administering the transcriptional inhibitor, cordycepin, to mature Arabidopsis leaves. We study changes in mRNA stability and translation during light stress and recovery. [ABSTRACT FROM AUTHOR]

SUMMARY: Photosynthetic efficiency and sink demand are tightly correlated with rates of phloem loading, where maintaining low cytosolic sugar concentrations is paramount to prevent the downregulation of photosynthesis. Sugars Will Eventually be Exported Transporters (SWEETs) are thought to have a pivotal role in the apoplastic phloem loading of C4 grasses. SWEETs have not been well studied in C4 species, and their investigation is complicated by photosynthesis taking place across two cell types and, therefore, photoassimilate export can occur from either one. SWEET13 homologues in C4 grasses have been proposed to facilitate apoplastic phloem loading. Here, we provide evidence for this hypothesis using the C4 grass Setaria viridis. Expression analyses on the leaf gradient of C4 species Setaria and Sorghum bicolor show abundant transcript levels for SWEET13 homologues. Carbohydrate profiling along the Setaria leaf shows total sugar content to be significantly higher in the mature leaf tip compared with the younger tissue at the base. We present the first known immunolocalization results for SvSWEET13a and SvSWEET13b using novel isoform‐specific antisera. These results show localization to the bundle sheath and phloem parenchyma cells of both minor and major veins. We further present the first transport kinetics study of C4 monocot SWEETs by using a Xenopus laevis oocyte heterologous expression system. We demonstrate that SvSWEET13a and SvSWEET13b are high‐capacity transporters of glucose and sucrose, with a higher apparent Vmax for sucrose, compared with glucose, typical of clade III SWEETs. Collectively, these results provide evidence for an apoplastic phloem loading pathway in Setaria and possibly other C4 species. [ABSTRACT FROM AUTHOR]

Epigenomic changes have been considered a potential missing link underlying phenotypic variation in quantitative traits but is potentially confounded with the underlying DNA sequence variation. Although the concept of epigenetic inheritance has been discussed in depth, there have been few studies attempting to directly dissect the amount of epigenomic variation within inbred natural populations while also accounting for genetic diversity. By using known genetic relationships between Brachypodium lines, multiple sets of nearly identical accession families were selected for phenotypic studies and DNA methylome profiling to investigate the dual role of (epi)genetics under simulated natural seasonal climate conditions. Despite reduced genetic diversity, appreciable phenotypic variation was still observable in the measured traits (height, leaf width and length, tiller count, flowering time, ear count) between as well as within the inbred accessions. However, with reduced genetic diversity there was diminished variation in DNA methylation within families. Mixed-effects linear modeling revealed large genetic differences between families and a minor contribution of DNA methylation variation on phenotypic variation in select traits. Taken together, this analysis suggests a limited but significant contribution of DNA methylation toward heritable phenotypic variation relative to genetic differences. [ABSTRACT FROM AUTHOR]