Date of Award

12-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Engineering and Earth Sciences

Committee Member

Dr. Paula Agudelo, Committee Co-chair

Committee Member

Dr. Christina Wells, Committee Co-chair

Committee Member

Dr. Christopher Saski

Committee Member

Dr. Hong Luo

Abstract

Reniform nematode (Rotylenchulus reniformis) is a semi-endoparasitic nematode that causes yield losses in numerous crops, including upland cotton (Gossypium hirsutum). Resistant cotton varieties are urgently needed, but the molecular basis of nematode-host plant interactions is poorly understood. To document plant responses to reniform nematode infection in upland cotton roots, we set up a split-root growth system to collect tissues from infected and uninfected portions of the same root system. A 12-day time course of histology and gene expression of infected roots were generated in Chapter 1. Results suggest reniform nematode infection induced protein synthesis and transport, inhibited cell division and plant defense pathways, and manipulated cell wall metabolism and plant hormone pathways. Histological observations recorded the developmental process of the permanent feeding structure, syncytium, induced by reniform nematode in pericycle cells. Pericyle cells are the same cells from which lateral roots emerge in upland cotton. In Chapter 2, we investigated the effect of reniform nematode parasitism on lateral root formation in upland cotton. Nematode infection resulted in significantly higher branching complexity in cotton roots and alters hormone-associated gene expression, particularly auxin. Reniform nematode-induced syncytia are characterized as regions of cell hypertrophy and cell wall dissolutions. In Chapter 3, monoclonal antibodies were used to investigate potential modifications of cell wall components in infected cotton roots. Fluorescence imaging revealed that syncytial cell walls contain low hemicellulose xyloglucan, but abundant highly methyl-esterified pectic homogalacturonan. Strong fluorescence of xyloglucan was overlapped with weak fluorescence of highly methyl-esterified pectic homogalacturonan, suggesting that, in reniform nematode-induced syncytia, pectate cross-links, instead of cellulose-xyloglucan network, possibly play a more important role in load-bearing within syncytium. In conclusion, we provide a broad transcriptomic overview of the compatible responses to reniform nematodes in susceptible upland cotton roots. Four hundred and eight five differentially expressed genes and 233 significantly enriched or depleted gene sets were identified.

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