The dynamics of Arabidopsis H2A.Z on SMALL AUXIN UP RNAs regulates abscisic acid-auxin signaling crosstalk

Extreme environmental changes threaten plant survival and worldwide food production. In response to osmotic stresses, plant hormone ABA activates stress responses and restricts plant growth. However, the epigenetic regulation of the ABA signaling and ABA-auxin crosstalk are not well known. Here we report that the histone variant H2A.Z knockdown mutant in Arabidopsis Col-0 ecotype, h2a.z-kd, has altered ABA signaling and stress performances. RNA-sequencing data showed that a majority of stress related genes are activated in h2a.z-kd. In addition, we revealed that ABA directly promotes the deposition of H2A.Z on SMALL AUXIN UP RNAs (SAURs), which is involved in ABA-repressed SAUR expression. Moreover, we found that ABA represses the transcription of H2A.Z genes through suppressing ARF7/19-HB22/25 module. Our results shed light on a dynamic and reciprocal regulation hub through H2A.Z deposition on SAURs and ARF7/19-HB22/25-mediated H2A.Z transcription to integrate ABA/auxin signaling and regulate stress responses in Arabidopsis.

ABA-dependent salt and drought stress improve strawberry fruit quality

Strawberry crop is very sensitive to osmotic stress conditions. We investigated the effect of the stress induced by mild drought (DS) and salt (SS) stresses, on molecular, physiological, and metabolic processes in the strawberry crop (Fragaria ananassa), cv. Camarosa. The results showed that the fruit yield was not affected. Mild DS and SS also resulted in an increased content of phenolics, anthocyanins, and l-ascorbic acid, and an increased antioxidant activity. These effects were accompanied by increased levels of ABA and its derivatives (phaseic and dehydrophasic acids), alongside the upregulation of several genes involved on their synthesis. Therefore, the results obtained in this study suggest that mild DS and SS improve the functional quality of strawberry fruits through and ABA-dependent mechanism.

Environmental nitrate signals through abscisic acid in the root tip

Roots respond to changes in environmental nitrate with a localized stimulation of ABA levels in the root tip. This rise in ABA levels is due to the action of ER-localized β-GLUCOSIDASE 1, which releases bioactive ABA from the inactive ABA-glucose ester. The slow rise in root tip ABA levels stimulates expression of nitrate metabolic enzymes and simultaneously activates a negative feedback loop involving the protein phosphatase, ABI2, which reduces nitrate influx via the AtNPF6.3 transceptor. The rise in root-tip localized ABA also negatively regulates expression of the SCARECROW transcription factor, thus providing a sensitive mechanism for modulating root growth in response to environmental changes.

ABA and cytokinins: challenge and opportunity for plant stress research

Accumulation of the stress hormone abscisic acid (ABA) induces many cellular mechanisms associated with drought resistance. Recent years have seen a rapid advance in our knowledge of how increased ABA levels are perceived by ABA receptors, particularly the PYL/RCAR receptors, but there has been relatively less new information about how ABA accumulation is controlled and matched to stress severity. ABA synthesis and catabolism, conjugation and deconjugation to glucose, and ABA transport all are involved in controlling ABA levels. This highly buffered system of ABA metabolism represents both a challenge and opportunity in developing a mechanistic understanding of how plants detect and respond to drought. Recent data have also shown that direct manipulation of cytokinin levels in transgenic plants has dramatic effect on drought phenotypes and prompted new interest in the role of cytokinins and cytokinin signaling in drought. Both ABA and cytokinins will continue to be major foci of drought research but likely with different trajectories both in terms of basic research and in translational research aimed at increasing plant performance during drought.

Exploring the interaction between small RNAs and R genes during Brachypodium response to Fusarium culmorum infection

The present study aims to investigate small RNA interactions with putative disease response genes in the model grass species Brachypodium distachyon. The fungal pathogen Fusarium culmorum (Fusarium herein) and phytohormone salicylic acid treatment were used to induce the disease response in Brachypodium. Initially, 121 different putative disease response genes were identified using bioinformatic and homology based approaches. Computational prediction was used to identify 33 candidate new miRNA coding sequences, of which 9 were verified by analysis of small RNA sequence libraries. Putative Brachypodium miRNA target sites were identified in the disease response genes, and a subset of which were screened for expression and possible miRNA interactions in 5 different Brachypodium lines infected with Fusarium. An NBS-LRR family gene, 1g34430, was polymorphic among the lines, forming two major genotypes, one of which has its miRNA target sites deleted, resulting in altered gene expression during infection. There were siRNAs putatively involved in regulation of this gene, indicating a role of small RNAs in the B. distachyon disease response.

Cytoplasmic degradation of the Arabidopsis transcription factor abscisic acid insensitive 5 is mediated by the RING-type E3 ligase KEEP ON GOING

To mitigate the effects of environmental stress the abscisic acid (ABA)-responsive transcription factor ABI5 is required to delay growth of germinated seedlings. In the absence of stress, KEEP ON GOING (KEG) E3 is required to maintain low levels of ABI5. However, the mechanism underlying KEG-dependent turnover of ABI5 is not known. In addition, localization studies place KEG at the trans-Golgi network, whereas ABI5 is nuclear. Here we show that KEG interacts directly with ABI5 via its conserved C3 region. Interactions between KEG and ABI5 were observed in the cytoplasm and trans-Golgi network only when the RING domain of KEG was inactivated or when ABI5 was stabilized via mutations. Deletion of the C-terminal region of ABI5 or substituting lysine 344 for alanine (K344A) prohibited protein turnover. Furthermore, ABI5 is observed in the cytoplasm of Arabidopsis thaliana root cells when the K344A mutation is combined with the deletion of a nuclear localization signal. Other lysine mutations (K353A, K364A, and K376A) in conjunction with the nuclear localization signal deletion did not result in cytoplasmic accumulation of ABI5. Loss of lysine 344 did not affect the ability of ABI5 to promote ABA responses, which demonstrates that the mutant transcription factor is still functional. Based on the results, a model is suggested where KEG targets ABI5 for degradation in the cytoplasm, thus reducing nuclear accumulation of the transcription factor in the absence of ABA.

Somatic embryogenesis inGnetum ula Brongn. (Gnetum edule) (Willd) Blume

Somatic embryos ofGnetum ula (Gnetum edule) an endangered gymnosperm closely related to the angiosperms have been induced in vitro. Megagametophyte tissue with immature embryos was cultured on Murashige and Skoog medium. A mucilaginous, translucent embryogenic callus was obtained with 5 mg/l BA. Callus induced with 2,4-D was non-embryogenic. The embryogenic callus in liquid half strength Murashige and Skoog medium without inorganic nitrates supplemented with 2.5 g/l casein hydrolysate and 0.5 g/l L-glutamine gave rise to immature embryos. The embryos matured when treated with 60 g/l sucrose and 10 mg/l abscisic acid.