Abstract
Worldwide, drought affects crop yields; therefore, understanding plants’ strategies to adapt to drought is critical. Chloroplasts are key regulators of plant responses, and signals from chloroplasts also regulate nuclear gene expression during drought. However, the interactions between chloroplast-initiated retrograde signals and ion channels under stress are still not clear. In this review, we summarise the retrograde signals that participate in regulating plant stress tolerance. We compare chloroplastic transporters that modulate retrograde signalling through retrograde biosynthesis or as critical components in retrograde signalling. We also discuss the roles of important plasma membrane and tonoplast ion transporters that are involved in regulating stomatal movement. We propose how retrograde signals interact with ion transporters under stress.
Highlights
The world will need to feed more than 9 billion people by 2050 [1], food production needs to increase by at least 70% [2]
Since chloroplast-initiated retrograde signals are involved in transducing various environmental stresses, and chloroplastic ion transporters are significant in regulating chloroplast status [84], do chloroplast ion transporters affect the generation of retrograde signals? Three general categories of proteins have been classified as ions transporters, i.e., channels/porins, primary transporters/pumps, and secondary transporters [85]; these have been shown to have important roles in photosynthesis
We summarised some retrograde signals that participate in the regulation of plant stress tolerance (Figure 1 and Table 1)
Summary
The world will need to feed more than 9 billion people by 2050 [1], food production needs to increase by at least 70% [2]. Plants protect themselves in the short term by closing stomata [8] and in the long term by increasing the root/shoot ratio [9], root hydraulic conductance [10], thickness of leaf cuticle [11], stomatal development [12], and cuticular wax [13] If these drought avoidance mechanisms are not successful, mechanisms to tolerate dehydration may be switched on. A chloroplast-initiated retrograde signalling pathway has been identified as having a significant role in regulating stomatal movement, which greatly affects plant drought tolerance [25,26]. PAP is produced in chloroplasts under drought stress to induce the expression of nuclear-encoded stress response genes, leading to stomatal closure [25,26]. We propose a potential interaction whereby chloroplasts sense drought and produce signals (e.g., PAP) which regulate stomatal movement to maintain water potential in plant cells and to guarantee a stable photosynthesis rate under drought
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