Date Published: April 11, 2017
Publisher: Public Library of Science
Author(s): You-Zhi Li, Xian-Wei Fan, Qiang Chen, Hao Zhong, Wei Wang.
Maize (Zea mays L.) is one of the major staple food crops of the world. However, high photoperiod sensitivity, especially for tropical germplasms, impedes attempts to improve maize agronomical traits by integration of tropical and temperate maize germplasms. Physiological and phenotypic responses of maize to photoperiod have widely been investigated based on multi-site field observations; however, proteome-based responsive mechanisms under controlled photoperiod regimes, nutrient and moisture soils are not yet well understood. In the present study, we sequenced and analyzed six proteomes of tropically-adapted and photoperiod-sensitive M9 inbred line at the vegetative 3 stage and proteomes from tropically-adapted and photoperiod-sensitive Shuang M9 (SM9) inbred line at the vegetative-tasseling stage. All plants were grown in growth chambers with controlled soil and temperature and three photoperiod regimes, a short photoperiod (SP) of 10 h light/14 h dark, a control neutral photoperiod (NP) of 12 h light/12 h dark, and a long photoperiod (LP) of 16 h light/8 h dark for a daily cycle. We identified 4,395 proteins of which 401 and 425 differentially-expressed proteins (DPs) were found in abundance in M9 leaves and in SM9 leaves as per SP/LP vs. NP, respectively. Some DPs showed responses to both SP and LP while some only responded to either SP or LP, depending on M9 or SM9. Our study showed that the photoperiodic response pathway, circadian clock rhythm, and high light density/intensity crosstalk with each other, but apparently differ from dark signaling routes. Photoperiod response involves light-responsive or dark-responsive proteins or both. The DPs positioned on the signaling routes from photoperiod changes to RNA/DNA responses involve the mago nashi homolog and glycine-rich RNA-binding proteins. Moreover, the cell-to-cell movement of ZCN14 through plasmodesmata is likely blocked under a 16-h-light LP. Here, we propose a photoperiodic model based on our findings and those from previous studies.
Photoperiod is a daily recurring pattern of light and dark periods . The response or capacity to respond to photoperiod is termed as photoperiodism . However, photoperiod sensing is also partially associated with mechanisms regulating the circadian rhythms [2–4].
In the present study, we sequenced only six proteomes from three photoperiods of which three proteomes were from the M9 inbred line at the V3 stage and three from SM9 inbred line at the VT stage respectively. GO categorization can show more information on biological processes and intracellular location. Therefore, our analysis of the proteome-based responsive mechanisms under controlled photoperiod regimes, nutrient and moisture soils was based on GO categorization of some of the DPs.
Based on our findings and evidence from previous studies, we propose a model that outlines and shows protein roadmaps and echoing routes in responses of maize to photoperiod changes (Fig 5). Our model emphasizes: (1) the biological processes of photoperiodic flowering signaling, photoperiod response, circadian rhythm, and high light density response could crosstalk with each other thorough a group of light-sensing proteins that may be clustered in the cell wall and/or plasma membrane; (2) signals of high light density likely occur under LP transmit; (3) the cell-to-cell movement of FT-like ZCN14 from the leaves into SAM through plasmodesmata is blocked under LP; (4) signaling of darkness is mediated by glutamate dehydrogenase, apparently independent of the other light signal transmission routes; and (5) changes in expression of the mago nashi homolog and the glycine-rich RNA-binding protein with photoperiods make an impact on splicing and nuclear export of mRNAs, and/or for RNA/DNA secondary structure unwinding; therefore, controlling the response of RNA/DNA to photoperiod changes.