Chaperone-like protein DAY plays critical roles in photomorphogenesis

Regulation of chloroplast biogenesis, development, and signaling by endogenous and exogenous cues

Chloroplasts are one of the defining features in most plants, primarily known for their unique property to carry out photosynthesis. Besides this, chloroplasts are also associated with hormone and metabolite productions. For this, biogenesis and development of chloroplast are required to be synchronized with the seedling growth to corroborate the maximum rate of photosynthesis following the emergence of seedlings. Chloroplast biogenesis and development are dependent on the signaling to and from the chloroplast, which are in turn regulated by several endogenous and exogenous cues. Light and hormones play a crucial role in chloroplast maturation and development. Chloroplast signaling involves a coordinated two-way connection between the chloroplast and nucleus, termed retrograde and anterograde signaling, respectively. Anterograde and retrograde signaling are involved in regulation at the transcriptional level and downstream modifications and are modulated by several metabolic and external cues. The communication between chloroplast and nucleus is essential for plants to develop strategies to cope with various stresses including high light or high heat. In this review, we have summarized several aspects of chloroplast development and its regulation through the interplay of various external and internal factors. We have also discussed the involvement of chloroplasts as sensors of various external environment stress factors including high light and temperature, and communicate via a series of retrograde signals to the nucleus, thus playing an essential role in plants' abiotic stress response.

Genome-wide identification of DnaJ gene family in Catalpa bungei and functional analysis of CbuDnaJ49 in leaf color formation

DnaJs are the common molecular chaperone proteins with strong structural and functional diversity. In recent years, only several DnaJ family members have been found to be able to regulate leaf color, and it remains to be explored whether there are other potential members that also regulate this character. Here, we identified 88 putative DnaJ proteins from Catalpa bungei, and classified them into four types according to their domain. Gene-structure analysis revealed that each member of CbuDnaJ family had same or similar exon-intron structure. Chromosome mapping and collinearity analysis showed that tandem and fragment duplication occurred in the process of evolution. Promoter analyses suggested that CbuDnaJs might be involved in a variety of biological processes. The expression levels of DnaJ family members in different color leaves of Maiyuanjinqiu were respectively extracted from the differential transcriptome. Among these, CbuDnaJ49 was the largest differentially expressed gene between the green and yellow sectors. Ectopic overexpression of CbuDnaJ49 in tobacco showed that the positive transgenic seedlings exhibited albino leaves, and the contents of chlorophyll and carotenoid were significantly reduced compared with those of wild type. The results suggested that CbuDnaJ49 played an important role in regulating leaf color. This study not only identified a novel gene of DnaJ family members regulating leaf color, but also provided new germplasm for landscaping.

J-like protein family of Arabidopsis thaliana: the enigmatic cousins of J-domain proteins

J-like proteins (JLPs) are emerging as ancillaries to the cellular chaperone network. They modulate functions of Hsp70:J-domain protein (JDP) systems in novel ways thereby having key roles in diverse plant processes. J-domain proteins (JDPs) form an obligate co-chaperone partnership with Hsp70s with their highly conserved J-domain to steer protein quality control processes in the cell. The HPD motif between helix II and helix III of the J-domain is crucial for JDP's interaction with Hsp70s. According to the most recent classification, J-like proteins (JLPs) form an extended class of the JDP family possessing a degenerate J-domain with the HPD motif non-conservatively replaced by other amino acid residues and hence are not able to interact with Hsp70s. Considering this most updated and acceptable JLP classification, we identified 21 JLPs in Arabidopsis thaliana that share a structurally conserved J-like domain (JLD), but lack the HPD motif. Analysis of publicly available gene expression data as well as real-time quantitative PCR performed for a few selected JLPs implicated some of these proteins in growth, development and stress response. Here, we summarize the current state of knowledge on plant JLPs and their involvement in vital plant cellular/metabolic processes, including chloroplast division, mitochondrial protein import and flowering. Finally, we propose possible modes of action for these highly elusive proteins and other DnaJ-related proteins (DNAJRs) in regulating the Hsp70 chaperone network.