Identification of new ABA- and MEJA-activated sugarcane bZIP genes by data mining in the SUCEST database.

Sugarcane is generally propagated by cuttings of the stalk containing one or more lateral buds, which will develop into a new plant. The transition from the dormant into the active stage constitutes a complex phenomenon characterized by changes in accumulation of phytohormones and several other physiological aspects. Abscisic acid (ABA) and methyl-jasmonate (MeJA) are major signaling molecules, which influence plant development and stress responses. These plant regulators modulate gene expression with the participation of many transcriptional factors. Basic leucine zipper proteins (bZIPs) form a large family of transcriptional factors involved in a variety of plant physiological processes, such as development and responses to stress. Query sequences consisting of full-length protein sequence of each of the Arabidopsis bZIP families were utilized to screen the sugarcane EST database (SUCEST) and 86 sugarcane assembled sequences (SAS) coding for bZIPs were identified. cDNA arrays and RNA-gel blots were used to study the expression of these sugarcane bZIP genes during early plantlet development and in response to ABA and MeJA. Six bZIP genes were found to be differentially expressed during development. ABA and MeJA modulated the expression of eight sugarcane bZIP genes. Our findings provide novel insights into the expression of this large protein family of transcriptional factors in sugarcane.

Glutathione S-transferase and aluminum toxicity in maize.

Aluminum (Al) toxicity induces changes in the expression of several genes, some of which are involved in plant responses to oxidative stress. Using mRNA differential display, we identified a maize Al-inducible cDNA encoding a glutathione S-transferase (GST). The gene was named GST27.2 owing to its homology to the maize gene GST27, which is known to be induced by xenobiotics. GST27.2 is present in the maize genome as a single copy and analysis of its expression pattern revealed that the gene is expressed mainly in the root tip. Expression was up-regulated in response to various Al and Cd concentrations in both Al-tolerant and Al-sensitive maize lines. Consistent with its role in plants, phylogenetic analysis of theta-type GSTs revealed that GST27.2 belongs to a group of proteins that respond to different stresses. Finally, structural analysis of the polypeptide chain indicates that the two amino acids that differ between GST27.2 and GST27 (E102K and P123L) could be responsible for alterations in activity and / or specificity. Together, these results suggest that GST27.2 may play an important part in plant defenses against Al toxicity.

RNA expression profiles and data mining of sugarcane response to low temperature.

Tropical and subtropical plants are generally sensitive to cold and can show appreciable variation in their response to cold stress when exposed to low positive temperatures. Using nylon filter arrays, we analyzed the expression profile of 1,536 expressed sequence tags (ESTs) of sugarcane (Saccharum sp. cv SP80-3280) exposed to cold for 3 to 48 h. Thirty-four cold-inducible ESTs were identified, of which 20 were novel cold-responsive genes that had not previously been reported as being cold inducible, including cellulose synthase, ABI3-interacting protein 2, a negative transcription regulator, phosphate transporter, and others, as well as several unknown genes. In addition, 25 ESTs were identified as being down-regulated during cold exposure. Using a database of cold-regulated proteins reported for other plants, we searched for homologs in the sugarcane EST project database (SUCEST), which contains 263,000 ESTs. Thirty-three homologous putative cold-regulated proteins were identified in the SUCEST database. On the basis of the expression profiles of the cold-inducible genes and the data-mining results, we propose a molecular model for the sugarcane response to low temperature.