Abstract
Polar auxin transport mediated by PIN-FORMED (PIN) proteins is critical for plant growth and development. As an environmental cue, shade stimulates hypocotyls, petiole, and stem elongation by inducing auxin synthesis and asymmetric distributions, which is modulated by PIN3,4,7 in Arabidopsis. Here, we characterize the MtPIN1 and MtPIN3, which are the orthologs of PIN3,4,7, in model legume species Medicago truncatula. Under the low Red:Far-Red (R:FR) ratio light, the expression of MtPIN1 and MtPIN3 is induced, and shadeavoidance response is disrupted in mtpin1 mtpin3 double mutant, indicating that MtPIN1 and MtPIN3 have a conserved function in shade response. Surprisingly, under the normal growth condition, mtpin1 mtpin3 displayed the constitutive shade avoidance responses, such as the elongated petiole, smaller leaf, and increased auxin and chlorophyll content. Therefore, MtPIN1 and MtPIN3 play dual roles in regulation of shadeavoidance response under different environments. Furthermore, these data suggest that PIN3,4,7 and its orthologs have evolved conserved and specific functions among species.
Highlights
As a key plant hormone, auxin regulates diverse aspects of plant growth and developmental processes
MtPIN1 and MtPIN3 were close to the subclade of Arabidopsis PIN3/PIN4/PIN7 (Supplementary Figure S1A) [26,27]
Both MtPIN1 and MtPIN3 were expressed in different organs and tissues including leaf, petiole, flower, root, and nodules, implying they play important roles in different developmental processes [27,28]
Summary
As a key plant hormone, auxin regulates diverse aspects of plant growth and developmental processes. Auxin is involved in the establishment and maintenance of apical dominance, phototropism, and gravitropism. Auxin plays a prominent role in regulating cell division and cellular expansion by altering cell wall plastics [1]. Auxin is mostly synthesized in young shoot tips and young leaves, and transported to recipient organs for modulating diverse developmental processes. PAT is mediated by three types of proteins: AUX1/LAX family [10], ABCB transporters [11,12,13] and PIN-FORMED (PIN) family of auxin efflux proteins [9,14]. PIN family auxin efflux carriers regulate PAT by altering their location at the plasma membrane to control the direction and quantity of auxin transportation [9,14]
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