Abstract

Root growth and distribution in the soil are key components that contribute to a plant's ability to thrive when water and nutrients are limited. As such, proper root hairs and lateral roots that are effectively distributed in the soil, both in density and depth, and well-developed root system can make effective use of available water and nutrients. In Arabidopsis, several Epidermal Patterning Factor (EPF) family members of small cysteine-rich peptides have been discovered as important signaling pathways which are recognized and perceived by the receptors encoded by the ERECTA gene family and TMM which possess diverse functions in controlling plant development are reported here to affect root hair development, lateral root densities and length, and primary root length.
In this research, the function of the EPFs and their putative receptors ERECTA and TMM in the development of root hairs, lateral roots, and primary roots were investigated under control and nitrate starvation conditions. These included EPF1, EPF2, EPFL4, EPFL5, EPFL6, EPFL9, ERECTA (ER), ERECTA like 1(ERL1), ERECTA Like 2 (ERL2), and TMM. In general, EPF2, EPFl4, EPFL5, EPFL6, ER, and ERL1were found to be positive regulators for root hair development, the mutation of these genes led to shortening the length and reducing the numbers of the root hairs, in contrast, epfl9i mutant developed longer and more root hairs suggesting EPFL9 was a negative regulator for root hair development. Six of these genes were discovered to function as negative regulators of primary root and lateral root development, the mutation of EPF2, EPFL4, EPFl5, EPFL6, ER and ERl2, and the overexpression lines for EPF2 and EPFL5 resulted in having longer primary and lateral root, also increasing the number of lateral roots.
Interestingly, only EPFL9 showed different response to nitrate starvation treatment compared to wild type, in which, nitrate starvation had stimulatory effect in wild-type and other mutants except for epfl9i which showed reduction in the number and length of the root hairs. Moreover, the wild- type lateral roots length and number remained unchanged in response to nitrate starvation, while nitrate starvation showed stimulatory effect on epfl9i and inhibitory effect on er for lateral root development. In addition, neither of the mutants and wild type showed any significant response to primary root length.