4.4 CRIR1 functions related to MeCSP5 in cassava
MeCSPs are nucleic acid-binding
proteins that contain both cold shock domain (CSD) and DNA-binding
domains, which have been widely found in bacteria, animals, and plants.
CSPs are important during cold shock response. Besides, the functions of
CSPs were first described in Escherichia coli (Goldstein, Pollitt &
Inouye, 1990). During cold stress, cell membrane fluidity and enzyme
activity decrease, and transcription and translation efficiency is
reduced to stabilize nucleic acid secondary structures. CSPs function as
RNA chaperones and counteract these harmful effects by destabilizing
secondary structures in target RNA at low temperatures, thus
facilitating the translation (Keto-Timonen, Hietala, Palonen, Hakakorpi,
Lindstrom & Korkeala, 2016). Arabidopsis AtCSP3 shares an
RNA chaperone function with Escherichia coli cold shock proteins
and positively regulates freezing tolerance through a non-CBFpathway (Kim et al., 2009). In this study, CRIR1 was showed to be
able to interact with MeCSP5, a homology protein of ArabidopsisAtCSP2 with 50% identity.. In addition, MeCSP5 protein exhibited
a similar cellular distribution pattern with CRIR1 transcripts
(Figure S2c). Although cold stress dramatically stimulated theMeCSP5 gene expression, its transcript level was not
significantly altered in the CRIR1 -overexpressors (Figure S2d),
suggesting that CRIR1 could regulate MeCSP5 at protein
level. In Arabidopsi s, AtCSP3 protein has been shown to interact
with a range of proteins in the nucleolus, nucleoplasm, and cytoplasm,
including ribosomal proteins, Gar1 RNA-binding protein, and mRNA
decapping protein. The results suggested that AtCSP3 participated in
multiple complexes and possibly regulated RNA processing and translation
(Kim, Sonoda, Sasaki, Kaminaka & Imai, 2013). One ribosomal protein was
found to interact with CRIR1 , indicating the possible involvement
of CRIR1 in ribosome biogenesis and protein translation.
Therefore, it will be interesting to determine if the complex that forms
with CRIR1 , MeCSP5 and other proteins regulates cold stress
tolerance in cassava by controlling the RNA unwinding activity or
facilitating mRNA translation.
Taken together, in this study, a total of 3 004 full-length lncRNAs in
cassava were identified, and 316 of them were further characterized as
cold-related lncRNAs. Functional analysis shows that CRIR1 can
confer cold stress tolerance and participate in MeCSP complexes to
enhance translation efficiency at low temperatures. The research has
provided a valuable source for studying full-length lncRNAs in cassava
and their corresponding candidate genes. CRIR1 , as a case in the
study, will provide applicable genetic resource for breeding cold
tolerant crops without yield penalty.