Root exudates mediate kin recognition in plants

Abstract

Though recent work has demonstrated that plants can recognize species, kin versus strangers, and self/non-self roots, no mechanism for identity recognition in plants has yet been found. Here we examined the role of soluble chemicals in signaling among roots. Utilizing Arabidopsis thaliana, we exposed young seedlings to liquid media containing exudates from siblings, strangers (non-siblings), or only their own exudates. In one experiment, root secretions were inhibited by sodium orthovanadate and root length and number of lateral roots were measured. In a second experiment, responses to siblings, strangers, and their own exudates were measured for several accessions (genotypes), and the traits of length of the longest lateral root and hypocotyl length were also measured. The exposure of plants to the root exudates of strangers induced greater lateral root formation than exposure of plants to sibling exudates. Stranger recognition was abolished upon treatment with the secretion inhibitor. In one experiment, plants exposed to sibling or stranger exudates have shorter roots than plants only exposed to their own exudates. This self/non-self recognition response was not affected by the secretion inhibitor. The results demonstrate that that kin recognition and self/non-self are two separate identity recognition systems involving soluble chemicals. Kin recognition requires active secretion by roots.

Keywords: Kin recognition; crosstalk; inhibitor; plants; roots; secretions; self/non-self; strangers.

Figure 1

Lateral roots in Arabidopsis thaliana plants grown solitary (OWN) or in sibling (KIN) and non-sibling (STRANGER) exudates from the secretion inhibitor experiment. (A) Shows the representative photographs of OWN, KIN and STRANGER seedlings in the control treatment. (B) Shows the representative photographs of OWN, KIN and STRANGER treatments in the sodium vanadate treatment. (C) Shows the average number of lateral roots among OWN, KIN and ortho STRANGER seedlings in control and sodium vanadate (Na₃VO₄ [3 µM]) treatments. Means with the same letter do not differ significantly. Ortho bars indicate mean± S.E. for N = 864.

Figure 2

Average length of primary roots in Arabidopsis thaliana plants grown solitary (OWN) or in sibling (KIN) and non-sibling (STRANGER) exudates from the secretion inhibitor experiment, for the control and sodium orthovanadate [Na₃VO₄ (3 µM)] treatments. Means with the same letter do not differ significantly. Bars indicate mean± S.E for N = 864.

Figure 3

Average lateral root number for eight accessions of A. thaliana in OWN (solitary), KIN (from siblings), and STRANGER (non-siblings) exudates. Trial 1 comprises CHA 11, CHA 38, trial 2 Col(0) and WS(0), and trial 3 CHA 28, CHA 31, CHA 34, and CHA 4. Average lateral root number is greater in Col(0) and WS (0) accessions than CHA accessions, but the effects of exudates did not differ among accession. Bars indicate means ± 1S.E for N = 216.

Figure 4

The panel A, B, C represents the experimental set up for OWN, KIN and STRANGER treatments. The arrows in the panel indicates the transfer of plants into exposure to KIN/STRANGER root exudates.