Abstract
CBL-interacting protein kinase (CIPK) family is a unique group of serine/threonine protein kinase family identified in plants. Among this family, AtCIPK23 and its homologs in some plants are taken as a notable group for their importance in ions transport and stress responses. However, there are limited reports on their roles in seedling growth and development, especially in Solanaceae plants. In this study, NtCIPK23, a homolog of AtCIPK23 was cloned from Nicotiana tabacum. Expression analysis showed that NtCIPK23 is mainly expressed in the radicle, hypocotyl, and cotyledons of young tobacco seedlings. The transcriptional level of NtCIPK23 changes rapidly and spatiotemporally during seed germination and early seedling growth. To study the biological function of NtCIPK23 at these stages, the overexpressing and CRISPR/Cas9-mediated knock-out (ntcipk23) tobacco lines were generated. Phenotype analysis indicated that knock-out of NtCIPK23 significantly delays seed germination and the appearance of green cotyledon of young tobacco seedling. Overexpression of NtCIPK23 promotes cotyledon expansion and hypocotyl elongation of young tobacco seedlings. The expression of NtCIPK23 in hypocotyl is strongly upregulated by darkness and inhibited under light, suggesting that a regulatory mechanism of light might underlie. Consistently, a more obvious difference in hypocotyl length among different tobacco materials was observed in the dark, compared to that under the light, indicating that the upregulation of NtCIPK23 contributes greatly to the hypocotyl elongation. Taken together, NtCIPK23 not only enhances tobacco seed germination, but also accelerate early seedling growth by promoting cotyledon greening rate, cotyledon expansion and hypocotyl elongation of young tobacco seedlings.
Highlights
Calcium (Ca2+) is a ubiquitous second messenger in the plant
Calcineurin B-like protein (CBL) always interact with CBL-interacting protein kinase (CIPK) family to form a complicated but flexible CBL-CIPK network [3,4]
CIPK family is a plant-specific class of serine/threonine protein kinase family, which was classified as Group 3 of the sucrose non-fermenting 1-related kinases (SnRK3) [6]
Summary
Calcium (Ca2+) is a ubiquitous second messenger in the plant. When plants are stimulated by environmental and developmental changes, the concentrations of intracellular Ca2+ changes spatially and temporally, and form diverse calcium signals that are sensed and decoded by different calcium sensors [1]. To identify its biological function, tobacco materials with different expression levels of NtCIPK23 were obtained and comparative phenotypic analysis during the early seedling growth and development was performed. Plants 2021, 10, 323 materials with different expression levels of NtCIPK23 were obtained and comparati3voef 15 phenotypic analysis during the early seedling growth and development was performed. FFiigguurree55..TThheepphheennoottyyppee aanndd ddaattaa aannaallyyssiiss ooff hhyyppooccoottyyll iinn ttoobbaaccccoo mmaatteerriiaallss wwiitthh ddiiffffeerreenntt NNttCCIIPPKK2233 eexxpprreessssiioonn lleevveellss.. Cotyledon is tthhe mmaaiinn ssttoorraaggee oorrggaann tthhaatt pprroovviiddeess nutrients for seed germination and early seedling growth, and it is aallso tthhee fifirrsstt oorrggaann for photosynthessiiss aafftteerrggeerrmmininaatitoionn[3[344].].ThTehrerfeofroer,ec,octyolteydleodnopnlapylsayascaritcirciatlicraolleroinlethine tehaerlyeasrtlaygsetaogf eseoefdsgeerdmgineramtioinnaatinodnsaenedlisnegedglrionwg tghr.oHwetrhe., iHt weraes, fitouwnads tfhoautntdhethexatprtehsesion level of NtCIPK23 was dramatically enhanced during cotyledon greening and reached a peak when the cotyledons were fully expanded (Figure 2b(V,VI)). Contributions of NtCIPK23 to hypocotyl elongation in this study suggested that the gene is of potential agronomic significance in the improvement of seedling emergence and uniformity, and it is quite necessary to deepen the knowledge of NtCIPK23 in seed germination and early seedling growth
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