Regulating Tradeoffs to Improve Rice Production

Abstract

Plants are sessile organisms that are continuously exposed to a wide range of environmental stresses. To cope with various stresses using limited resources, plants have evolved diverse mechanisms of "tradeoff" that enable the allocation of resources to address the most life-threatening stress. During our studies on induced disease resistance in rice, we have found some important phenomena relevant to tradeoffs between biotic and abiotic stress responses, and between stress response and plant growth. We characterized these tradeoff phenomena from viewpoints of signaling crosstalks associated with transcriptional regulation. Here, I describe following topics: (1) PTP1-dependent increased disease susceptibility of rice under low temperature and high salinity conditions, (2) OsNPR1-dependent tradeoff between pathogen defense and photosynthesis, (3) tradeoff between pathogen defense and abiotic stress tolerance in WRKY45-overexpressing rice plants, and (4) WRKY62-dependent tradeoff between pathogen defense and hypoxia tolerance. Lastly, I discuss my view regarding the significance of such tradeoffs in agricultural production that should be considered in crop breeding; that is, the tradeoffs, although they benefit plants in nature, can be rather disadvantageous in agricultural production.

Keywords: OsNPR1; WRKY45; WRKY62; pathogen defense; photosynthesis; rice; stress tolerance; tradeoff.

FIGURE 1

Tradeoffs involving the salicylic acid pathway in rice. (A) Tradeoff between pathogen defense and abiotic stress tolerance mediated by protein tyrosine phosphatase. WRKY45 is phosphorylated and activated by OsMPK6 in response to chemical defense inducers. OsMPK6 is inactivated following tyrosine dephosphorylation by protein tyrosine phosphatase, which is mediated by ABA, in response to cold stress. This leads to hypo-phosphorylation and inactivation of WRKY45. (B) Tradeoff between pathogen defense and photosynthesis mediated by OsNPR1. OsNPR1 downregulates chloroplastic activity resulting in a decreased photosynthetic rate, while it upregulates the expression of defense genes. (C) Tradeoff between pathogen defense and submergence tolerance mediated by WRKY62. Following the activation of the salicylic acid pathway, WRKY45 and WRKY62 form heterodimers that activate DPF transcription. Upon submergence, only WRKY62 is produced, resulting in the formation of homodimers that repress DPF expression. Molecule X represents a presumptive transcription factor that binds to a hypoxia-responsive element in the promoter of hypoxia-responsive genes, possibly as a heterodimer with WRKY62.