The auxin transporter, OsAUX1, is involved in primary root and root hair elongation and in Cd stress responses in rice (Oryza sativa L.)

Abstract

These authors contributed equally to this work. SUMMARYAuxin and cadmium (Cd) stress play critical roles during root development. There are only a few reports on the mechanisms by which Cd stress influences auxin homeostasis and affects primary root (PR) and lateral root (LR) development, and almost nothing is known about how auxin and Cd interfere with root hair (RH) development. Here, we characterize rice osaux1 mutants that have a longer PR and shorter RHs in hydroponic culture, and that are more sensitive to Cd stress compared to wild-type (Dongjin). OsAUX1 expression in root hair cells is different from that of its paralogous gene, AtAUX1, which is expressed in non-hair cells. However, OsAUX1, like AtAUX1, localizes at the plasma membrane and appears to function as an auxin tranporter. Decreased auxin distribution and contents in the osaux1 mutant result in reduction of OsCyCB1;1 expression and shortened PRs, LRs and RHs under Cd stress, but may be rescued by treatment with the membrane-permeable auxin 1-naphthalene acetic acid. Treatment with the auxin transport inhibitors 1-naphthoxyacetic acid and N-1-naphthylphthalamic acid increased the Cd sensitivity of WT rice. Cd contents in the osaux1 mutant were not altered, but reactive oxygen species-mediated damage was enhanced, further increasing the sensitivity of the osaux1 mutant to Cd stress. Taken together, our results indicate that OsAUX1 plays an important role in root development and in responses to Cd stress.

Transcriptome Analysis of Cadmium-Treated Roots in Maize (Zea mays L.)

“…Additionally, changes in root architecture also improve the tolerance of Cd stress in plants (Yu et al, 2015; Li P. et al, 2016). In Arabidopsis , the primary root length was decreased under Cd stress (Hu et al, 2013).…”

“…For example, in Arabidopsis , Cd alleviates Cd-induced inhibition of root growth by altering the expression of auxin transport genes, such as PIN1 , PIN2 , PIN4 , and AUX1 (Hu et al, 2013; Li P. et al, 2016). The auxin transporter, OsAUX1, is involved in root system development and in Cd stress responses in rice (Yu et al, 2015). In our study, two auxin efflux transporter genes ( ZmPIN4 and ZmPIN5 ) and two auxin influx transporter genes ( ZmLAX1 and ZmLAX3 ) were responsive to Cd stress ( Figure 4B ).…”

“…The results indicated that the reduction in root growth by 50 μM Cd was considerably enhanced by NAA application and was alleviated by the addition of 1-NOA ( Figure 6a – d ). In rice, exogenous NAA treatment improves Cd tolerance in osaux1 mutant, the local auxin gradients provided by OsAUX1 are essential for Cd tolerance (Yu et al, 2015). The inhibition of auxin transport by 1-NOA reduced the physiological responses caused by Cd stress, suggesting a close relationship between auxin transport and the Cd stress responses.…”

The regulation and plasticity of root hair patterning and morphogenesis

“…Root hairs of wer mutants can be restored to wild-type length by auxin application, supporting the assumption that auxin supply from non-hair cells is required for proper root hair elongation (Jones et al, 2009). In the rice osaux1 mutant, too, root hairs are considerably shorter than those of the wild type (Yu et al, 2015). In contrast to its Arabidopsis ortholog, OsAUX1 is expressed in root hairs but not in non-hair cells, probably reflecting the different patterning of root hairs of the two species (Yu et al, 2015).…”

“…In the rice osaux1 mutant, too, root hairs are considerably shorter than those of the wild type (Yu et al, 2015). In contrast to its Arabidopsis ortholog, OsAUX1 is expressed in root hairs but not in non-hair cells, probably reflecting the different patterning of root hairs of the two species (Yu et al, 2015). As we discuss below, a number of studies have investigated how auxin might influence the various stages of root hair development.…”