Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 23, 2009
Publication Date: August 31, 2009
Citation: Macarisin, D., Wisniewski, M.E., Bassett, C.L., Thannhauser, T.W. 2009. Proteomic analysis of B-aminobutyric acid priming and aba-induction of drought resistance in crabapple (Malus pumila): effect on general metabolism, the phenylpropanoid pathway and cell wall enzymes. Plant Cell and Environment. 32: 1612-1631. Interpretive Summary: Environmental stress is a primary cause for crop losses and reductions in yield worldwide. It is not uncommon for losses to exceed 50% of expected yields. In particular, drought represents a significant problem to growing fruit crops and all crops in general. Taking into account the projections of global warming, water stress will increasingly become more of a problem. Significant research is being conducted to identify the genetic regulation of drought tolerance so that it can be manipulated either through breeding or genetic transformation technologies. However, it is also important to explore the use of management practices that can increase drought tolerance as well, especially since drought resistance can be difficult to balance with the need for continued growth. We have evaluated the ability of a chemical, beta-aminobutyric acid (BABA), to induce drought tolerance in crabapple seedlings. This unique compound has been shown to establish resistance to both abiotic and biotic stress in many model plants. BABA accomplishes this by sensitizing the plant to stress so that it responds very rapidly once the stress is applied rather than by inducing immediate changes in gene expression that may slow down or stop growth. The effect of BABA was compared with the hormone abscisic acid (ABA) which is known to close stomates and stop growth. Additionally, we conducted a comprehensive examination of the proteins (proteome) that were expressed in the treated seedlings in order to develop a better understanding of the biochemical mechanisms associated with drought tolerance. Results indicated that the application of BABA as a root drench could provide drought tolerance to crabapple seedlings without immediately shutting down growth and photosynthesis as in ABA-treated seedlings. While ABA- and BABA-treated seedlings exhibited similar changes in their proteomes, there were some changes that were unique to the BABA treatment. In particular, a suppression of lignin biosynthesis and an increase in the enzyme, pectin methylesterase, was seen. We postulate that these changes in cell-wall-related proteins allow the plant to withstand the negative pressures of transpiration experienced during water stress without becoming too rigid which would stop growth. The use of BABA may represent a new management tool for helping plants to withstand water stress, especially during transplanting, and is an excellent tool for studying mechanisms of drought tolerance in woody plants.
Technical Abstract: In a variety of annual crops and model plants, the xenobiotic compound, DL-beta-aminobutyric acid (BABA), has been shown to enhance disease resistance and increase salt, drought, and thermotolerance. BABA does not activate stress genes directly but rather sensitizes plants to respond more quickly and strongly to biotic and abiotic stresses. This process is referred to as chemical priming. There are no reports, however, on BABA-induced abiotic stress resistance in woody plants. Additionally, the metabolic pathways through which BABA mediates both abiotic and biotic stress resistance are still being elucidated. In the present study, drought tolerance of six-week-old crabapple (Malus pumila) seedlings was significantly increased (P xi 0.05) following a soil drench treatment with 500 micro M BABA. 2-D Difference in-Gel Electrophoresis (DIGE) was employed to characterize and compare differences in protein expression in leaf tissue sampled from control, BABA-primed and ABA-treated seedlings exposed to drought stress. A comparison of the different treatment combinations on the third and tenth day of dehydration revealed that 32 and 138 proteins, respectively, were differentially regulated by (3)1.5-fold in at least one condition. Among these proteins, some showed almost identical patterns of up-regulation or down-regulation in both BABA and ABA treated seedlings. This finding supports the general concept that BABA-induced abiotic stress resistance in plants is achieved by potentiating an ABA-regulated pathway. Some proteins, however, were uniquely up-regulated and down-regulated only in BABA-primed plants, indicating that BABA may also mediate resistance via some ABA-independent pathways. MALDI-TOF MS/MS was utilized to identify proteins of interest. Based on the putative function of the identified proteins, we propose metabolic pathways that may be involved in the resistance response of crabapple to water deficit. Suppression of lignin biosynthesis and photosynthesis, an increase in cell wall stiffening via activation of pectin methyl esterases, up-regulation of proteins that stabilize the photosynthesis apparatus, an increase in energy metabolism and in S-adenosyl-L-methionine synthetases levels that may be involved in accumulation of compatible solutes are suggested as possible mechanisms involved in BABA-primed drought tolerance in crabapple seedlings. In summary, BABA-treated seedlings were more resistant to water deficit than controls but not ABA-treated seedlings. While there was similarity between changes in the proteome of ABA and BABA-treated seedlings, a dramatic shift in the proteome occurred earlier in ABA-treated seedlings. Presumably, this had the effect of slowing growth more rapidly in ABA-treated seedlings. BABA appears to have potential as a management tool to increase drought tolerance in woody plants and to develop a more comprehensive understanding of the mechanisms underlying drought resistance.