Final Report Summary - CAPX IN HS SIGNALING (Role of cytosolic ascorbate-peroxidases (cAPXs) in heat stress (HS) perception and in systemic HS-signaling)
Each year crop yields are severely impacted by a variety of stress conditions, including heat, cold, drought, hypoxia, and salt. Unfortunately, this deleterious trend is expected to continue due to global warming and increase desertification of agricultural land, while global population and demand for land increases.
The current research program is part of the major efforts of the Miller lab to study how plants perceive abiotic stresses and rapidly respond to them both locally and systemically to achieve acclimation and protection. More specifically, the lab studies the involvement of reactive oxygen species (ROS) as signaling molecules mediating the acclimation responses of plants to environmental stresses. The research aims at understanding the roles of ROS scavenging enzymes that regulate the ROS signal and to discover genes responding to the signal that play important role in the stress tolerance.
In this CIG project we have been studying the role of the three cytosoloic ascorbate peroxidase (cAPX) (APX1, APX2 and APX6), H2O2 scavenging enzymes in the acclimation response of plants to heat stress. Of the three cAPXs APX1 and APX2 have been previously studied and their role during stress has been considered well understood, yet major gaps still exist in the current knowledge of APX1 and APX2 function in signaling and stress response in plants. In contrast with APX1 and APX2, very little was known about the function and expression of APX6, as it has not been studied prior to our project. Evidently, our recent studies, summarized herein, also exposed. Our study aimed to better understand the division of labor between the three cAPXs and provide new insight into the function of in Arabidopsis abiotic stress response. We further sought to study the general involvement of ROS in heat stress response acclimation by using new molecular approach and novel tools developed during the study. The study involved generation of new combinations of double and triple mutant plants for cAPXs, transgenic Arabidopsis reporter lines expressing heat stress responsive transcription factor (MBF1c) and heat shock transcription factors fused to fluorescent proteins that can be used for following the development and progression of the response to heat in real-time. However, the major progress has been the identification of novel role of APX2 and APX6 in protection of the reproductive stage and seeds, respectively.
APX2 deficient mutant was found to enhance seed production during HS, while the vegetative stages of the plant were less tolerant to the stress compared to the wild type. Genetic and physiologic analyses, revealed the male gametophyte (the pollen grain) of the apx2 mutant acquired heat stress tolerance during both development on the mother plant as well as during fertilization, while the ovule was not more tolerant than the wild type. The new discovery advanced this part of the research toward identification of pollen-specific genes and mechanisms that enhance tolerance in these HS sensitive developmental phases.
APX6 was found to function during seed development and during germination, protecting against oxidative, osmotic and heat stresses. Further more mutants deficient in APX6 showed increased accumulation of ROS as well as the plant hormones ABA and auxin.
These two hormones play a pivotal role in controlling seed dormancy. The study further, discovered a novel crosstalk between ROS and these plant hormones, which most likely is mediated through the transcription factor ABI4. The study of APX2 and APX6 resulted in three publications already, two additional manuscripts are currently being prepared and more are expected in the near future. Due to the great progress made in the research of APX2 and APX6, the focus of the study shifted during the 3rd year to invest more to promote identification of genes and pathways related to stress response and tolerance in pollen and seeds.
Our advancement in studying the role of cAPXs in Arabidopsis brought us closer to identifying mechanisms that render acclimation to seeds during their development as well as pollen, two extremely sensitive phases of plant life cycle. With knowledge further gain we would be in a position to try and manipulate thermotolerance of these stress-vulnerable stages in crop plants.
The current research program is part of the major efforts of the Miller lab to study how plants perceive abiotic stresses and rapidly respond to them both locally and systemically to achieve acclimation and protection. More specifically, the lab studies the involvement of reactive oxygen species (ROS) as signaling molecules mediating the acclimation responses of plants to environmental stresses. The research aims at understanding the roles of ROS scavenging enzymes that regulate the ROS signal and to discover genes responding to the signal that play important role in the stress tolerance.
In this CIG project we have been studying the role of the three cytosoloic ascorbate peroxidase (cAPX) (APX1, APX2 and APX6), H2O2 scavenging enzymes in the acclimation response of plants to heat stress. Of the three cAPXs APX1 and APX2 have been previously studied and their role during stress has been considered well understood, yet major gaps still exist in the current knowledge of APX1 and APX2 function in signaling and stress response in plants. In contrast with APX1 and APX2, very little was known about the function and expression of APX6, as it has not been studied prior to our project. Evidently, our recent studies, summarized herein, also exposed. Our study aimed to better understand the division of labor between the three cAPXs and provide new insight into the function of in Arabidopsis abiotic stress response. We further sought to study the general involvement of ROS in heat stress response acclimation by using new molecular approach and novel tools developed during the study. The study involved generation of new combinations of double and triple mutant plants for cAPXs, transgenic Arabidopsis reporter lines expressing heat stress responsive transcription factor (MBF1c) and heat shock transcription factors fused to fluorescent proteins that can be used for following the development and progression of the response to heat in real-time. However, the major progress has been the identification of novel role of APX2 and APX6 in protection of the reproductive stage and seeds, respectively.
APX2 deficient mutant was found to enhance seed production during HS, while the vegetative stages of the plant were less tolerant to the stress compared to the wild type. Genetic and physiologic analyses, revealed the male gametophyte (the pollen grain) of the apx2 mutant acquired heat stress tolerance during both development on the mother plant as well as during fertilization, while the ovule was not more tolerant than the wild type. The new discovery advanced this part of the research toward identification of pollen-specific genes and mechanisms that enhance tolerance in these HS sensitive developmental phases.
APX6 was found to function during seed development and during germination, protecting against oxidative, osmotic and heat stresses. Further more mutants deficient in APX6 showed increased accumulation of ROS as well as the plant hormones ABA and auxin.
These two hormones play a pivotal role in controlling seed dormancy. The study further, discovered a novel crosstalk between ROS and these plant hormones, which most likely is mediated through the transcription factor ABI4. The study of APX2 and APX6 resulted in three publications already, two additional manuscripts are currently being prepared and more are expected in the near future. Due to the great progress made in the research of APX2 and APX6, the focus of the study shifted during the 3rd year to invest more to promote identification of genes and pathways related to stress response and tolerance in pollen and seeds.
Our advancement in studying the role of cAPXs in Arabidopsis brought us closer to identifying mechanisms that render acclimation to seeds during their development as well as pollen, two extremely sensitive phases of plant life cycle. With knowledge further gain we would be in a position to try and manipulate thermotolerance of these stress-vulnerable stages in crop plants.