Protein profiles reveal diverse responsive signaling pathways in kernels of two maize inbred lines with contrasting drought sensitivity

Abstract

Drought stress is a major factor that contributes to disease susceptibility and yield loss in agricultural crops. To identify drought responsive proteins and explore metabolic pathways involved in maize tolerance to drought stress, two maize lines (B73 and Lo964) with contrasting drought sensitivity were examined. The treatments of drought and well water were applied at 14 days after pollination (DAP), and protein profiles were investigated in developing kernels (35 DAP) using iTRAQ (isobaric tags for relative and absolute quantitation). Proteomic analysis showed that 70 and 36 proteins were significantly altered in their expression under drought treatments in B73 and Lo964, respectively. The numbers and levels of differentially expressed proteins were generally higher in the sensitive genotype, B73, implying an increased sensitivity to drought given the function of the observed differentially expressed proteins, such as redox homeostasis, cell rescue/defense, hormone regulation and protein biosynthesis and degradation. Lo964 possessed a more stable status with fewer differentially expressed proteins. However, B73 seems to rapidly initiate signaling pathways in response to drought through adjusting diverse defense pathways. These changes in protein expression allow for the production of a drought stress-responsive network in maize kernels.

Figure 1

Functional classification of the identified proteins. The pie chart shows the distribution of drought-responsive proteins into their functional classes in percentage. (A) Drought-responsive proteins in B73; and (B) Drought-responsive proteins in Lo964.

Figure 2

Venn diagram representing the overlap of the identified proteins in abundance with or without drought stress treatments in drought-tolerant maize line Lo964 and drought-sensitive maize line B73. (A) Up-regulation of proteins under drought stress; and (B) Down-regulation of proteins under drought stress.

Figure 3

Hierarchical clustering of drought stress responsive proteins involved in cell rescue/defense and redox homeostasis (A), protein metabolism (B), hormone responsive, signal transduction, transcription factor and membrane transport (C) and carbohydrate metabolism and storage proteins (D). Hierarchical cluster analysis was conducted using the Cluster 3.0 (University of Tokyo, Tokyo, Japan) and Treeview software (University of Glasgow, Scotland, UK).

Figure 4

Protein-protein interaction networks analyzed by String software. (A) Network analyzed from drought responsive proteins in Lo964 under drought stress condition; (B) Network analyzed from drought responsive proteins in B73 under drought stress condition. Different line colors represent types of evidence for association: Green line, neighborhood evidence; pink line, fusion evidence; purple line, experimental evidence; light blue line, database evidence; black line, coexpression evidence; blue line, co-occurrence evidence; and yellow line, text-mining evidence. The networks indicated by broken oval shapes represent the functional modules.

Figure 5

A schematic of drought stress responses in kernels of the two examined maize lines, Lo964 with an extensive, deep and strong lateral root system [16,56] and B73 with a superficial, fewer lateral root system [18,59].