The HD-Zip I transcription factor HaHB4 produces an increment in xylem vasculature by repressing the auxin transporter LAX2

MORENO-PIOVANO GUILLERMO S.; MORENO JAVIER E.; CABELLO JULIETA V.; ARCE AGUSTÍN L.; CHAN RAQUEL L.

Foz de Iguazú

Congreso; 11th International Congress of Plant Molecular Biology; 2015

Fundación ArgenINTA

HaHB4, an HDZIP type I protein from Helianthus annuus, improves agronomic traits related to water deprivation in Arabidopsis and other crop transgenic plants. Ectopic expression of HaHB4 in Arabidopsis induces a complex phenotype including improved water use efficiency, delayed senescence and enhanced resistance to herbivory. The molecular mechanism underlying HaHB4 technology is largely unknown. Using a bioinformatic approach, we identified the auxin influx carrier LAX2 as part of a set of HaHB4-regulated genes with the potential to modulate water use efficiency. LAX2 gene expression is down-regulated in HaHB4 overexpressing plants both in microarray and qPCR experiments. Given the importance of vascular tissues in water transport and considering that several HDZIP type III transcription factors are involved in vascular development, we decided to explore the phenotype of lax2 mutant plants. Two different mutant alleles of LAX2 showed an increment in xylem vasculature, including both cell number and size. Concomitantly, Arabidopsis plants ectopically expressing HaHB4 showed an increment in both phloem and xylem vasculature. In consonance with the role of xylem in water transport, we observed that lax2 mutants consume significantly less water during a mild water stress treatment compared to the WT genotype. Taken together, these observations connect auxin transport to the enhanced water use efficiency induced by HaHB4 in Arabidopsis and other crop plants and report the ability of this HDZIP I protein to modulate vascular development.