Characterization of APX and APX-R gene family in Brassica juncea and B. rapa for tolerance against abiotic stresses

APX and APX-R gene families were identified and characterized in two important oilseed species of Brassica. Gene expression under abiotic stress conditions, recombinant protein expression, and analysis further divulged their drought, heat, and salt-responsive behavior. Ascorbate peroxidases (APX) are heme-dependent enzymes that rid the cells of H₂O₂ and regulate diverse biological processes. In the present study, we performed APX gene family characterization in two Brassica sp. (B. juncea and B. rapa) as these are commercially important oilseed crops and affected severely by abiotic stresses. We identified 16 BjuAPX and 9 BraAPX genes and 2 APX-R genes each in B. juncea and B. rapa genomes, respectively. Phylogenetic analysis divided the APX genes into five distinct clades, which exhibited conservation in the gene structure, motif organization, and sub-cellular location within the clade. Structural analysis of APX and APX-R proteins revealed the amino acid substitutions in conserved domains of APX-R proteins. The expression profiling of BjuAPX and BraAPX genes showed that 3 BjuAPX, 7BraAPX, and 2 BraAPX-R genes were drought and heat responsive. Notably, BjuAAPX1a, BjuAPX1d, BjuAAPX6, BraAAPX1a, BraAAPX2, and BraAAPX3b showed high expression levels in RT-qPCR. Cis-regulatory elements in APX and APX-R gene promoters supported the differential behavior of these genes. Further, two stress-responsive genes BjuAPX1d and BraAAPX2 were cloned, characterized, and their roles were validated under heat, drought, salt, and cold stress in bacterial expression system. This study for the first time reports the presence of APX activity in dimeric and LMW form of purified BraAAPX2 protein. The study may help pave way for developing abiotic stress-tolerant Brassica crops.

Proteome-wide and lysine crotonylation profiling reveals the importance of crotonylation in chrysanthemum (Dendranthema grandiforum) under low-temperature

BACKGROUND

Low-temperature severely affects the growth and development of chrysanthemum which is one kind of ornamental plant well-known and widely used in the world. Lysine crotonylation is a recently identified post-translational modification (PTM) with multiple cellular functions. However, lysine crotonylation under low-temperature stress has not been studied.

RESULTS

Proteome-wide and lysine crotonylation of chrysanthemum at low-temperature was analyzed using TMT (Tandem Mass Tag) labeling, sensitive immuno-precipitation, and high-resolution LC-MS/MS. The results showed that 2017 crotonylation sites were identified in 1199 proteins. Treatment at 4 °C for 24 h and - 4 °C for 4 h resulted in 393 upregulated proteins and 500 downregulated proteins (1.2-fold threshold and P < 0.05). Analysis of biological information showed that lysine crotonylation was involved in photosynthesis, ribosomes, and antioxidant systems. The crotonylated proteins and motifs in chrysanthemum were compared with other plants to obtain orthologous proteins and conserved motifs. To further understand how lysine crotonylation at K136 affected APX (ascorbate peroxidase), we performed a site-directed mutation at K136 in APX. Site-directed crotonylation showed that lysine decrotonylation at K136 reduced APX activity, and lysine complete crotonylation at K136 increased APX activity.

CONCLUSION

In summary, our study comparatively analyzed proteome-wide and crotonylation in chrysanthemum under low-temperature stress and provided insights into the mechanisms of crotonylation in positively regulated APX activity to reduce the oxidative damage caused by low-temperature stress. These data provided an important basis for studying crotonylation to regulate antioxidant enzyme activity in response to low-temperature stress and a new research ideas for chilling-tolerance and freezing-tolerance chrysanthemum molecular breeding.

Selection of flooding stress tolerant sweetpotato cultivars based on biochemical and phenotypic characterization

Sweetpotato [Ipomoea batatas (L.) Lam] serves as a sustainable food source and ensures nutrition security in the face of climate change. Recently, farmers have developed increased interest in replacing rice with sweetpotato in paddy fields for higher income. However, sweetpotato is more susceptible to flooding stress than other abiotic stresses including drought and salinity. Here, we selected flooding tolerant sweetpotato cultivars based on biochemical characterization. Young seedlings of 33 sweetpotato cultivars were subjected to flooding stress for 20 days, and Yeonjami (YJM) was identified as the most flooding tolerant sweetpotato cultivar. Plant growth and biochemical characteristics of YJM were compared with those of Jeonmi (JM), a flooding sensitive sweetpotato cultivar. Under flooding stress, YJM showed higher content of chlorophyll and lower inhibition of plant height and fibrous root length than JM. Biochemical characterization revealed that although malondialdehyde and hydrogen peroxide contents were increased in fibrous roots of both cultivars, the amount of increase was 4-fold lower in YJM than in JM. Additionally, leaves of YJM showed higher ascorbate peroxidase activity than those of JM under flooding stress. Our results suggest that high membrane stability and antioxidant capacity are important flooding tolerance factors in sweetpotato. Furthermore, several flooding tolerance-related genes involved in starch and sucrose metabolism, fermentation, and cell wall loosening showed earlier induction and higher transcript levels in YJM leaves and fibrous roots than in JM tissues under flooding stress. Thus, phenotypic and biochemical characterization suggests that YJM could be used as a flooding tolerant sweetpotato cultivar.