New Phytologist

Jurdak, Rana; Rodrigues, Guilherme de Almeida Garcia; Chaumont, Nicole; Schivre, Geoffrey; Bourbousse, Clara; Barneche, Fredy; Bou Dagher Kharrat, Magda; Bailly, Christophe

doi: 10.1111/nph.18038pmid: 35175638

Reactive oxygen species (ROS) release seed dormancy through an unknown mechanism. We used different seed dormancy‐breaking treatments to decipher the dynamics and localization of ROS production during seed germination. We studied the involvement of ROS in the breaking of Arabidopsis seed dormancy by cold stratification, gibberellic acid (GA3) and light. We characterized the effects of these treatments on abscisic acid and gibberellins biosynthesis and signalling pathways. ROS, mitochondrial redox status and peroxisomes were visualized and/or quantified during seed imbibition. Finally, we performed a cytogenetic characterization of the nuclei from the embryonic axes during seed germination. We show that mitochondria participate in the early ROS production during seed imbibition and that a possible involvement of peroxisomes in later stages should still be analysed. At the time of radicle protrusion, ROS accumulated within the nucleus, which correlated with nuclear expansion and chromatin decompaction. Taken together, our results provide evidence of the role of ROS trafficking between organelles and of the nuclear redox status in the regulation of seed germination by dormancy.

Wu, Lin‐Bo; Eom, Joon‐Seob; Isoda, Reika; Li, Chenhao; Char, Si Nian; Luo, Dangping; Schepler‐Luu, Van; Nakamura, Masayoshi; Yang, Bing; Frommer, Wolf B.

doi: 10.1111/nph.18054pmid: 35211968

SWEETs play important roles in intercellular sugar transport. Induction of SWEET sugar transporters by Transcription Activator‐Like effectors (TALe) of Xanthomonas ssp. is key for virulence in rice, cassava and cotton. We identified OsSWEET11b with roles in male fertility and potential bacterial blight (BB) susceptibility in rice. While single ossweet11a or 11b mutants were fertile, double mutants were sterile. As clade III SWEETs can transport gibberellin (GA), a key hormone for spikelet fertility, sterility and BB susceptibility might be explained by GA transport deficiencies. However, in contrast with the Arabidopsis homologues, OsSWEET11b did not mediate detectable GA transport. Fertility and susceptibility therefore are likely to depend on sucrose transport activity. Ectopic induction of OsSWEET11b by designer TALe enabled TALe‐free Xanthomonas oryzae pv. oryzae (Xoo) to cause disease, identifying OsSWEET11b as a potential BB susceptibility gene and demonstrating that the induction of host sucrose uniporter activity is key to virulence of Xoo. Notably, only three of six clade III SWEETs are targeted by known Xoo strains from Asia and Africa. The identification of OsSWEET11b is relevant for fertility and for protecting rice against emerging Xoo strains that target OsSWEET11b.

Castañeda, Laura; Giménez, Estela; Pineda, Benito; García‐Sogo, Begoña; Ortiz‐Atienza, Ana; Micol‐Ponce, Rosa; Angosto, Trinidad; Capel, Juan; Moreno, Vicente; Yuste‐Lisbona, Fernando J.; Lozano, Rafael

doi: 10.1111/nph.18034pmid: 35170044

CRABS CLAW (CRC) orthologues play a crucial role in floral meristem (FM) determinacy and gynoecium formation across angiosperms, the key developmental processes for ensuring successful plant reproduction and crop production. However, the mechanisms behind CRC mediated FM termination are far from fully understood. Here, we addressed the functional characterization of tomato (Solanum lycopersicum) paralogous CRC genes. Using mapping‐by‐sequencing, RNA interference and CRISPR/Cas9 techniques, expression analyses, protein–protein interaction assays and Arabidopsis complementation experiments, we examined their potential roles in FM determinacy and carpel formation. We revealed that the incomplete penetrance and variable expressivity of the indeterminate carpel‐inside‐carpel phenotype observed in fruit iterative growth (fig) mutant plants are due to the lack of function of the S. lycopersicum CRC homologue SlCRCa. Furthermore, a detailed functional analysis of tomato CRC paralogues, SlCRCa and SlCRCb, allowed us to propose that they operate as positive regulators of FM determinacy by acting in a compensatory and partially redundant manner to safeguard the proper formation of flowers and fruits. Our results uncover for the first time the physical interaction of putative CRC orthologues with members of the chromatin remodelling complex that epigenetically represses WUSCHEL expression through histone deacetylation to ensure the proper termination of floral stem cell activity.

doi: 10.1111/nph.17489pmid: N/A

Dani, Kaidala Ganesha Srikanta; Loreto, Francesco

doi: 10.1111/nph.18035pmid: 35170033

Some canonical plant hormones such as auxins and gibberellins have precursors that are biogenic volatiles (indole, indole acetonitrile, phenylacetaldoxime and ent‐kaurene). Cytokinins, abscisic acid and strigolactones are hormones comprising chemical moieties that have distinct volatile analogues, and are synthesised alongside constitutively emitted volatiles (isoprene, sesquiterpenes, lactones, benzenoids and apocarotenoid volatiles). Nonvolatile hormone analogues and biogenic volatile organic compounds (BVOCs) evolved in tandem as growth and behavioural regulators in unicellular organisms. In plants, however, nonvolatile hormones evolved as regulators of growth, development and differentiation, while endogenous BVOCs (often synthesised lifelong) became subtle regulators of hormone synthesis, availability, activity and turnover, all supported by functionally redundant components of hormone metabolism. Reciprocal changes in the abundance and activity of hormones, nitric oxide, and constitutive plant volatiles constantly bridge retrograde and anterograde signalling to maintain hormone equilibria even in unstressed plants. This is distinct from transient interference in hormone signalling by stress‐induced and exogenously received volatiles.

Perico, Chiara; Tan, Sovanna; Langdale, Jane A.

doi: 10.1111/nph.17955pmid: 35020214

Organisation and patterning of the vascular network in land plants varies in different taxonomic, developmental and environmental contexts. In leaves, the degree of vascular strand connectivity influences both light and CO2 harvesting capabilities as well as hydraulic capacity. As such, developmental mechanisms that regulate leaf venation patterning have a direct impact on physiological performance. Development of the leaf venation network requires the specification of procambial cells within the ground meristem of the primordium and subsequent proliferation and differentiation of the procambial lineage to form vascular strands. An understanding of how diverse venation patterns are manifest therefore requires mechanistic insight into how procambium is dynamically specified in a growing leaf. A role for auxin in this process was identified many years ago, but questions remain. In this review we first provide an overview of the diverse venation patterns that exist in land plants, providing an evolutionary perspective. We then focus on the developmental regulation of leaf venation patterns in angiosperms, comparing patterning in eudicots and monocots, and the role of auxin in each case. Although common themes emerge, we conclude that the developmental mechanisms elucidated in eudicots are unlikely to fully explain how parallel venation patterns in monocot leaves are elaborated.

Carvalho, Carter; Davis, Rochelle; Connallon, Tim; Gleadow, Roslyn M.; Moore, Joslin L.; Uesugi, Akane

doi: 10.1111/nph.18018pmid: 35118675

Geographical variation in the environment underpins selection for local adaptation and evolutionary divergence among populations. Because many environmental conditions vary across species' ranges, identifying the specific environmental variables underlying local adaptation is profoundly challenging. We tested whether natural selection mediated by aridity predicts clinal divergence among invasive populations of capeweed (Arctotheca calendula) that established and spread across southern Australia during the last two centuries. Using common garden experiments with two environmental treatments (wet and dry) that mimic aridity conditions across capeweed’s invasive range, we estimated clinal divergence and effects of aridity on fitness and multivariate phenotypic selection in populations sampled along aridity gradients in Australia. We show that: (1) capeweed populations have relatively high fitness in aridity environments similar to their sampling locations; (2) the magnitude and direction of selection strongly differs between wet and dry treatments, with drought stress increasing the strength of selection; and (3) differences in directional selection between wet and dry treatments predict patterns of clinal divergence across the aridity gradient, particularly for traits affecting biomass, flowering phenology and putative antioxidant expression. Our results suggest that aridity‐mediated selection contributes to trait diversification among invasive capeweed populations, possibly facilitating the expansion of capeweed across southern Australia.

Wu, Di; Guo, Jianping; Zhang, Qian; Shi, Shaojie; Guan, Wei; Zhou, Cong; Chen, Rongzhi; Du, Bo; Zhu, Lili; He, Guangcun

doi: 10.1111/nph.18012pmid: 35119102

The planthopper resistance gene Bph6 encodes a protein that interacts with OsEXO70E1. EXO70 forms a family of paralogues in rice. We hypothesized that the EXO70‐dependent trafficking pathway affects the excretion of resistance‐related proteins, thus impacting plant resistance to planthoppers. Here, we further explored the function of EXO70 members in rice resistance against planthoppers. We used the yeast two‐hybrid and co‐immunoprecipitation assays to identify proteins that play roles in Bph6‐mediated planthopper resistance. The functions of the identified proteins were characterized via gene transformation, plant resistance evaluation, insect performance, cell excretion observation and cell wall component analyses. We discovered that another EXO70 member, OsEXO70H3, interacted with BPH6 and functioned in cell excretion and in Bph6‐mediated planthopper resistance. We further found that OsEXO70H3 interacted with an S‐adenosylmethionine synthetase‐like protein (SAMSL) and increased the delivery of SAMSL outside the cells. The functional impairment of OsEXO70H3 and SAMSL reduced the lignin content and the planthopper resistance level of rice plants. Our results suggest that OsEXO70H3 may recruit SAMSL and help its excretion to the apoplast where it may be involved in lignin deposition in cell walls, thus contributing to rice resistance to planthoppers.

Balch, William M.; Drapeau, David T.; Godrijan, Jelena

doi: 10.1111/nph.18009pmid: 35226360

Dani, Kaidala Ganesha Srikanta; Pollastri, Susanna; Pinosio, Sara; Reichelt, Michael; Sharkey, Thomas D.; Schnitzler, Jörg‐Peter; Loreto, Francesco

doi: 10.1111/nph.17833pmid: 34716577

Isoprene, a major biogenic volatile hydrocarbon of climate‐relevance, indisputably mitigates abiotic stresses in emitting plants. However functional relevance of constitutive isoprene emission in unstressed plants remains contested. Isoprene and cytokinins (CKs) are synthesized from a common substrate and pathway in chloroplasts. It was postulated that isoprene emission may affect CK‐metabolism. Using transgenic isoprene‐emitting (IE) Arabidopsis and isoprene nonemitting (NE) RNA‐interference grey poplars (paired with respective NE and IE genotypes), the life of individual IE and NE leaves from emergence to abscission was followed under stress‐free conditions. We monitored plant growth rate, aboveground developmental phenotype, modelled leaf photosynthetic energy status, quantified the abundance of leaf CKs, analysed Arabidopsis and poplar leaf transcriptomes by RNA‐sequencing in presence and absence of isoprene during leaf senescence. Isoprene emission by unstressed leaves enhanced the abundance of CKs (isopentenyl adenine and its precursor) by > 200%, significantly upregulated genes coding for CK‐synthesis, CK‐signalling and CK‐degradation, hastened plant development, increased chloroplast metabolic rate, altered photosynthetic energy status, induced early leaf senescence in both Arabidopsis and poplar. IE leaves senesced sooner even in decapitated poplars where source–sink relationships and hormone homeostasis were perturbed. Constitutive isoprene emission significantly accelerates CK‐led leaf and organismal development and induces early senescence independent of growth constraints. Isoprene emission provides an early‐riser evolutionary advantage and shortens lifecycle duration to assist rapid diversification in unstressed emitters.