Regulation of Arabidopsis Matrix Metalloproteinases by Mitogen-Activated Protein Kinases and Their Function in Leaf Senescence

The kinase ATM delays Arabidopsis leaf senescence by stabilizing the phosphatase MKP2 in a phosphorylation-dependent manner

Arabidopsis thaliana (Arabidopsis) Ataxia Telangiectasia Mutated (ATM) kinase plays a vital role in orchestrating leaf senescence; however, the precise mechanisms remain elusive. Here, our study demonstrates that ATM kinase activity is essential for mitigating age- and reactive oxygen species-induced senescence, as restoration of wild-type ATM reverses premature senescence in the atm mutant, while a kinase-dead ATM variant is ineffective. ATM physically interacts with and phosphorylates Mitogen-Activated Protein Kinase Phosphatase 2 (MKP2) to enhance stability under oxidative stress. Mutations in putative phosphorylation sites S15/154 on MKP2 disrupt its phosphorylation, stability, and senescence-delaying function. Moreover, mutation of mitogen-activated protein kinase 6, a downstream target of MKP2, alleviates the premature senescence phenotype of the atm mutant. Notably, the dual-specificity protein phosphatase 19 (HsDUSP19), a predicted human counter protein of MPK2, interacts with both ATM and HsATM and extends leaf longevity in Arabidopsis when overexpressed. These findings elucidate the molecular mechanisms underlying the role of ATM in leaf senescence and suggest that the ATM-MKP2 module is likely evolutionarily conserved in regulating the aging process across eukaryotes.

The DYRKP1 kinase regulates cell wall degradation in Chlamydomonas by inducing matrix metalloproteinase expression

The cell wall of plants and algae is an important cell structure that protects cells from changes in the external physical and chemical environment. This extracellular matrix, composed of polysaccharides and glycoproteins, must be constantly remodeled throughout the life cycle. However, compared to matrix polysaccharides, little is known about the mechanisms regulating the formation and degradation of matrix glycoproteins. We report here that a plant kinase belonging to the DUAL-SPECIFICITY TYROSINE PHOSPHORYLATION-REGULATED KINASE (DYRK) family present in all eukaryotes regulates cell wall degradation after mitosis of Chlamydomonas reinhardtii by inducing the expression of matrix metalloproteinases (MMPs). Without the plant DYRK kinase (DYRKP1), daughter cells cannot disassemble parental cell walls and remain trapped inside for more than 10 days. On the other hand, the DYRKP1 complementation line shows normal degradation of the parental cell wall. Transcriptomic and proteomic analyses indicate a marked down-regulation of MMP gene expression and accumulation, respectively, in the dyrkp1 mutants. The mutants deficient in MMPs retain palmelloid structures for a longer time than the background strain, like dyrkp1 mutants. Our findings show that DYRKP1, by ensuring timely MMP expression, enables the successful execution of the cell cycle. Altogether, this study provides insight into the life cycle regulation in plants and algae.

Root transcriptomic provides insights on molecular mechanisms involved in the tolerance to water deficit in Pisum sativum inoculated with Pseudomonas sp

MAIN CONCLUSION

Root transcriptomics and biochemical analyses in water-stressed Pisum sativum plants inoculated with Pseudomonas spp. suggested preservation of ABA-related pathway and ROS detoxification, resulting in an improved tolerance to stress. Drought already affects agriculture in large areas of the globe and, due to climate change, these areas are predicted to become increasingly unsuitable for agriculture. For several years, plant growth-promoting bacteria (PGPB) have been used to improve legume yields, but many aspects of this interaction are still unclear. To elucidate the mechanisms through which root-associated PGPB can promote plant growth in dry environments, we investigated the response of pea plants inoculated with a potentially beneficial Pseudomonas strain (PK6) and subjected to two different water regimes. Combined biometric, biochemical, and root RNA-seq analyses revealed that PK6 improved pea growth specifically under water deficit, as inoculated plants showed an increased biomass, larger leaves, and longer roots. Abscisic acid (ABA) and proline quantification, together with the transcriptome analysis, suggested that PK6-inoculated plant response to water deficit was more diversified compared to non-inoculated plants, involving alternative metabolic pathways for the detoxification of reactive oxygen species (ROS) and the preservation of the ABA stress signaling pathway. We suggest that the metabolic response of PK6-inoculated plants was more effective in their adaptation to water deprivation, leading to their improved biometric traits. Besides confirming the positive role that PGPB can have in the growth of a legume crop under adverse conditions, this study offers novel information on the mechanisms regulating plant-bacteria interaction under varying water availability. These mechanisms and the involved genes could be exploited in the future for the development of legume varieties, which can profitably grow in dry climates.

Recent advances in cellular degradation and nuclear control of leaf senescence

Senescence is the final stage of plant growth and development, and is a highly regulated process at the molecular, cellular, and organismal levels. When triggered by age, hormonal, or environmental cues, plants actively adjust their metabolism and gene expression to execute the progression of senescence. Regulation of senescence is vital for the reallocation of nutrients to sink organs, to ensure reproductive success and adaptations to stresses. Identification and characterization of hallmarks of leaf senescence are of great importance for understanding the molecular regulatory mechanisms of plant senescence, and breeding future crops with more desirable senescence traits. Tremendous progress has been made in elucidating the genetic network underpinning the metabolic and cellular changes in leaf senescence. In this review, we focus on three hallmarks of leaf senescence - chlorophyll and chloroplast degradation, loss of proteostasis, and activation of senescence-associated genes (SAGs), and discuss recent findings of the molecular players and the crosstalk of senescence pathways.